Cathelicidins are antimicrobial peptides (AMPs) that were first discovered to have microbicidal properties but more recently to be multifunctional immunomodulators and thus important in influencing host defence against infectious disease. Whilst roles in various organs have been demonstrated, their expression patterns in health and disease in other organs are less clear and their key immunomodulatory functions remain undefined, particularly with regard to the balance of immunomodulatory properties and microbicidal activity in their ability to promote defence against infection. I therefore set out to describe LL-37 expression (human cathelicidin) in the female reproductive tract (across the menstrual cycle) and in the lung (during specific lung diseases), to define the effects on the function of airway epithelial cells during bacterial infection and to evaluate the key in vivo roles of endogenous cathelicidin (using a knockout mouse model) as well as the effect of therapeutic administration of LL-37 in a pulmonary Pseudomonas aeruginosa infection model. I demonstrated that cathelicidin protein and transcription shows a cyclical pattern of expression in female reproductive tissues which is maintained at high levels in decidua. LL- 37 protein was also detected in hTERT endometrial epithelial cells but despite the suggestion that cathelicidin may be regulated by steroid hormones there was no direct effect of progesterone on transcription. LL-37 is barely detected in healthy airways however is well known to increase during infection or inflammation. I observed that sputum from patients with bronchiectasis showed a correlation between the level of LL-37, TNF, MPO and chronic colonisation of Pseudomonas aeruginosa. Patients with lung cancer expressed much less LL- 37 than the bronchiectasis patients but there was a trend towards increased production postsurgery compared to pre-surgery. LL-37 was previously shown by our lab to selectively promote BAX and caspase-dependant death of infected epithelial cells. I went on to show that this appears to be a partially caspase- 1 dependent mechanism and that human bronchial epithelial (HBE) cells and A549 cell lines both express several of the components required to form inflammasomes, a caspase-1 dependant form of inflammatory cell death. Finally, I showed using murine models that cathelicidin enhances bacterial clearance during pulmonary infection in vivo, a response which is defective in mice lacking endogenous cathelicidin and that administration of exogenous, synthetic LL-37 at the time of infection can promote an early protective neutrophil influx in the absence of endogenous cathelicidin production.

Cathelicidins (CATHLs) are small, cationic antimicrobial peptides that establish an early innate immune defense against infections in mammals. Beyond their wide spectrum of antimicrobial activity, these peptides play important roles in wound repair, chemotactic activity, and apoptosis. Thus, comprehensive characterizing of bovine CATHLs could potentially identify underlying inherited differences in innate immunity and disease resistance in cattle. The purpose of the present study was to verify the placement of the CATHL cluster at the distal end of bovine chromosome 22 (BTA22), identify any single nucleotide polymorphisms (SNPs) and insertion-deletion (indel) polymorphisms within the gene family, explore copy number variation, and investigate the functional impact any of these variants may have in overall bovine innate immunity. A framework radiation hybrid map was constructed with 7 markers screened against the bovine 12,000 rad whole genome RH (12K WG-RH) panel, which when compared to the current genome assembly (Btau_4.0) confirmed current gene order. Comparative sequence analysis for 10 domestic cattle breeds representing both Bos taurus taurus and Bos taurus indicus revealed 60 SNPs, 7 of which were nonsynonymous, and 5 indel mutations. Data from array comparative genomic hybridization (aCGH) between four Angus and four Nelore animals showed a 2-fold increase in copy number of the CATHL4 locus, which was verified by quantitative PCR (qPCR) of genomic DNA. Nelore animals showed an approximate 2-fold increase in the CATHL4 gene. Subsequently, the expression of CATHL4 in Nelore neutrophils exhibited a range of 2- to 5-fold increases in CATHL4 gene expression. Finally, a colorimetric bactericidal assay was performed on the neutrophils of the same Angus and Nelore animals previously genotyped for copy number variations (CNVs). After in vitro challenges to Staphylococcus aureus, Salmonella typhimurium, Mannheimia haemolytica, and Pasteurella multocida, the killing capacity of Nelore neutrophils was approximately 20 percent greater than Angus neutrophils for M. haemolytica and 10 percent greater for P. multocida. Characterization of this antimicrobial gene family is central to developing a firm understanding regarding the effects CATHL variation has with respect to bovine innate immunity.

宿主防御肽，如抗菌肽和防御素，是固有性免疫的重要组成部分。LL-37是由37个残基组成的阳离子宿主防御肽，是目前唯一被发现的人源宿主防御肽。它在不同的生物过程中都起着关键作用。新证据表明，LL-37与肿瘤进展也有关系。在许多类型的人类恶性肿瘤中它有不同表达，但在结肠癌中的表达和作用，仍未知。在此，我们将对LL-37及其17至32残基片断（ 简称FK-16）对结肠癌的影响进行研究。 / 免疫组化染色结果表明，LL-37在人类结肠癌组织中的表达比正常组织有显著减少。并且，LL-37的表达与TUNEL阳性细胞数量呈正比。合成的LL-37能够诱导不同的结肠癌细胞发生不依赖半胱天冬酶激活的凋亡细胞死亡。并且，LL-37通过激活p53下调Bcl2及上调Bax与Bak来诱导凋亡。LL-37也促使肿瘤坏死因子和核酸内切酶G 向核内转移，以其为目标的siRNA沉默能使细胞对LL-37诱导的凋亡呈现出耐受现象。更重要的是，LL-37的促凋亡作用被发现可以通过对百日咳敏感的Gαi蛋白偶联受体来介导。同时，宿主防御肽敲除的小鼠肠黏膜中，p53、Bax和Bak表达减少而Bcl2表达增加，凋亡的基础水平量也减少。由此说明，LL-37可通过激活GPCR-p53-Bax / Bak / Bcl-2的新信号级联反应来激活AIF / EndoG调控的结肠癌细胞凋亡。 / 与LL-37类似，其片断FK-16也促使不同结肠癌细胞株死亡。但其死亡诱导机制与LL-37不尽相同。FK-16引发了一种独特的死亡方式，即初始诱导不依赖半胱天冬酶激活的凋亡之后紧随引发自噬性细胞死亡。而LL-37没有明显引起这种自噬性死亡。孵育FK-16 24小时后，结肠癌细胞被证明发生凋亡。延长孵育至48小时，细胞的生化和形态学体征符合自噬，包括增加LC3阳性自噬体，积累酸性自噬泡与自溶酶体，和提高 LC3-II水平。敲除两个自噬有关基因 ATG5 和ATG7, 能够部分逆转由FK-16所引起的细胞死亡。并且，细胞凋亡和细胞自噬机制相关信号通路之间存在的交叉调控，在此研究中也被深入提及。 / Host defense peptides, such as cathelicidins (LL-37) and defensins, are important components in the innate immunity. LL-37, a human cationic host defense peptide composed of 37 residues, is the only cathelicidin described so far in humans. It plays a key role in diverse biological processes, including natural immunity, inflammation and tissue repair. Emerging evidence suggests that LL-37 is implicated in cancer development. In this regard, the expression of LL-37 is found to be dysregulated in many types of human malignancy, including lung, breast, ovarian, and gastric cancers. The expression and function of LL-37 in colon cancer, however, are still unknown. In this thesis, the roles of LL-37 and its 17-32 fragment (hereafter referred to as FK-16) in colon cancer development were investigated. / By immunohistochemical staining, it is demonstrated that the expression of LL-37 was significantly reduced in human colon cancer tissues as compared with the cancer adjacent normal tissues. Moreover, LL-37 expression was positively correlated with the number of TUNEL-positive cells. Furthermore, synthetic LL-37 induced caspase-independent apoptotic cell death in different cultured colon cancer cells. In this connection, LL-37 induced apoptosis via downregulation of Bcl-2 and upregulation of Bak and Bax in a p53-dependent manner. It also induced the upregulation and nuclear translocation of apoptosis-inducing factor (AIF) and endonuclease G (EndoG), whose targetings by siRNAs rendered the cells resistant to LL-37-induced apoptosis. Above all, the pro-apoptotic effect of LL-37 was found to be mediated through a pertussis toxin-sensitive Gαi protein-coupled receptor. Concordantly, colonic mucosa of cathelicidin-knockout mice exhibited reduced expression of p53, Bax and Bak and increased expression of Bcl-2 together with a lower basal level of apoptosis. Taken together, we demonstrated that LL-37 activates a novel signaling cascade involving the GPCR-p53-Bax/Bak/Bcl-2 axis to activate AIF/EndoG-mediated apoptosis in colon cancer cells. / Similar to the effect of LL-37 peptide, the fragment FK-16 also induced cell death in colon cancer cell lines. However, the action is different. Results demonstrated that FK-16 triggered a unique pattern of cell death characterized by initial caspase-independent apoptosis followed by autophagic cell death, the latter of which was not observed obviously in cells treated with LL-37. Treating colon cancer cells with FK-16 for 24 h induced apoptosis as evidenced by phosphatidylserine externalization, chromatin condensation and DNA fragmentation. Prolonged treatment with FK-16 induced biochemical and morphological features consistent with autophagy, including increased formation of LC3+ autophagosomes, the accumulation of acidic vesicular organelles and autolysosomes, and increased levels of LC3-I/II, Atg5 and Atg7. Knockdown of Atg5 or Atg7 partially reversed the cytotoxic effect of FK-16, suggesting that FK-16-induced autophagy was pro-death in nature. Furthermore, the novel cross-talks between apoptotic and autophagic signalings were also noted. / Collectively, the present study not only contributes to understanding the role of host defense peptide cathelicidin in tumorigenesis, but also provides pre-clinical evidence to propel the development and application of these peptides as novel therapeutic agents for the treatment of colon cancer. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / 综上所述，目前的研究不仅有助于理解宿主防御肽在肿瘤发生, 同时也提供了临床前研究证据，推动了宿主防御肽的开发和应用, 这些肽片段为治疗结肠癌提供了新的治疗手段 。 / Ren, Shunxiang. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references (leaves 176-208). / Abstract also in Chinese. / Abstract (English) --- p.i / Abstract (Chinese) --- p.iv / Declaration --- p.vi / Acknowledgements --- p.vii / Publications --- p.ix / Table of contents --- p.xiii / List of illustrations --- p.xviii / Abbreviations --- p.xxiii / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Colorectal cancer --- p.1 / Chapter 1.1.1 --- Epidemiology of colorectal cancer --- p.1 / Chapter 1.1.2 --- Etiology of colorectal cancer --- p.3 / Chapter 1.1.3 --- Pathogenesis of CRC --- p.8 / Chapter 1.1.4 --- Chemotherapy of colorectal cancer --- p.9 / Chapter 1.2 --- Programmed cell death (PCD) --- p.10 / Chapter 1.2.1 --- Cell death --- p.10 / Chapter 1.2.2 --- Apoptosis --- p.11 / Chapter 1.2.2.1 --- Mechanisms of apoptosis --- p.12 / Chapter 1.2.2.1.1 --- Caspase-dependent apoptosis --- p.13 / Chapter 1.2.2.1.2 --- Caspase-independent apoptosis --- p.15 / Chapter 1.2.2.1.3 --- Tumor suppressor p53 --- p.17 / Chapter 1.2.2.2 --- G-coupled protein receptors in apoptosis --- p.18 / Chapter 1.2.3.1 --- Types of Autophagy --- p.20 / Chapter 1.2.3.2 --- Biological process --- p.22 / Chapter 1.2.3.3 --- Biological functions --- p.24 / Chapter 1.2.3.4 --- Autophagic machinery --- p.27 / Chapter 1.2.3.5 --- Autophagy in cancer --- p.30 / Chapter 1.2.3.6 --- Autophagy and apoptosis --- p.32 / Chapter 1.3 --- Biological functions of cathelicidin --- p.33 / Chapter 1.3.1 --- Antimicrobial activity --- p.34 / Chapter 1.3.2 --- Immunological functions --- p.35 / Chapter 1.3.3 --- Wound healing, angiogenesis and mitogenesis --- p.36 / Chapter 1.3.4 --- Programmed cell death --- p.38 / Chapter 1.4 --- Aim of the present study --- p.39 / Chapter Chapter 2 --- Methods / Chapter 2.1 --- General --- p.41 / Chapter 2.1.1 --- Chemicals and reagents --- p.41 / Chapter 2.1.2 --- Antibodies --- p.44 / Chapter 2.1.3 --- Commercial kits --- p.45 / Chapter 2.1.4 --- Peptide synthesis --- p.46 / Chapter 2.1.5 --- Experimental Animals --- p.46 / Chapter 2.1.6 --- Cell Culture --- p.47 / Chapter 2.2 --- DNA Methylation Analysis --- p.48 / Chapter 2.2.1 --- 5-aza-2’-deoxycytidine (5’Aza-dC) Treatment --- p.48 / Chapter 2.2.2 --- Bisulfite Genomic Sequencing and Methylated-DNA capture (MethylCap)-qPCR --- p.48 / Chapter 2.3 --- Effects of LL-37 and its analogue FK-16 in colon cancer cells in vitro --- p.48 / Chapter 2.3.1 --- Cell viability Assay --- p.49 / Chapter 2.3.2 --- Lactic dehydrogenase (LDH) activity --- p.49 / Chapter 2.3.3 --- Cell cycle analysis --- p.49 / Chapter 2.3.4 --- Measurement of apoptosis in vitro --- p.50 / Chapter 2.3.4.1 --- Quantitation of DNA fragmentation --- p.50 / Chapter 2.3.4.2 --- Quantitation of phosphatidylserine externalization --- p.50 / Chapter 2.3.5 --- Reverse Transcription Polymerase Chain Reaction (RT-PCR) --- p.51 / Chapter 2.3.6 --- Nuclear protein extraction --- p.52 / Chapter 2.3.7 --- Western Blot --- p.53 / Chapter 2.3.8 --- Immunofluorescence --- p.54 / Chapter 2.3.9 --- Bcl-2 overexpression --- p.54 / Chapter 2.3.9.1 --- Transforming competent cells --- p.55 / Chapter 2.3.9.2 --- Plasmid DNA purification --- p.55 / Chapter 2.3.10 --- RNA interference --- p.56 / Chapter 2.3.11 --- Detection of acidic vesicular organelles (AVOs) with acridine orange --- p.57 / Chapter 2.3.12 --- Labeling of autophagic vacuoles with monodansylcadaverine (MDC) --- p.58 / Chapter 2.3.13 --- Transmission electron microscopy --- p.59 / Chapter 2.4 --- Cathelicidin-knockout (Cnlp/) mice model --- p.60 / Chapter 2.4.1 --- Normal mouse colon sample collection --- p.60 / Chapter 2.4.2 --- Tissue Processing --- p.61 / Chapter 2.4.3 --- Measurement of basal apoptosis in normal colon tissues --- p.61 / Chapter 2.5 --- Clinical samples --- p.62 / Chapter 2.5.1 --- Immunohistochemistry of clinical samples --- p.62 / Chapter 2.5.2 --- Measurement of colonocyte apoptosis of clinical samples --- p.62 / Chapter 2.5.3 --- Evaluation of colonocyte proliferation of clinical samples --- p.63 / Chapter 2.6 --- Statistical analysis --- p.63 / Chapter Chapter 3 --- Results and Discussion / Chapter 3.1 --- LL-37 was downregulated in colon cancer tissues --- p.64 / Chapter 3.2 --- Effects of LL-37 on human colon cancer cells --- p.72 / Chapter 3.2.1 --- LL-37 induced DNA fragmentation and phosphatidylserine externalization without caspase activation in colon cancer cells --- p.72 / Chapter 3.2.2 --- LL-37 induced AIF- and EndoG-dependent apoptosis --- p.79 / Chapter 3.2.3 --- Altered expression of Bcl-2 family members was required for AIF- and EndoG-mediated apoptosis induced by LL-37 --- p.84 / Chapter 3.2.4 --- p53 activation was required for LL-37-induced apoptosis --- p.90 / Chapter 3.2.5 --- The apoptogenic action of LL-37 was mediated by G protein-coupled receptor (GPCR) --- p.94 / Chapter 3.2.6 --- Reduced basal apoptotic rate in colonic mucosa of cathelicidin-knockout mice --- p.95 / Chapter 3.2.7 --- Preliminary Discussion --- p.103 / Chapter 3.3 --- Effects of FK16 on human cancer cells --- p.108 / Chapter 3.3.1 --- FK-16 induced AIF- and EndoG-dependent apoptosis in colon cancer cells --- p.108 / Chapter 3.3.2 --- FK-16 induced autophagic cell death in colon cancer cells --- p.116 / Chapter 3.3.3 --- Activation of p53 was required for FK-16-indcued apoptosis and autophagy cell death --- p.123 / Chapter 3.3.4 --- Altered expression of Bcl-2 and Bax was required for FK-16-indcued apoptosis and autophagic cell death --- p.129 / Chapter 3.3.5 --- FK-16-induced apoptosis and autophagic cell death were reciprocally regulated --- p.134 / Chapter 3.3.6 --- Preliminary Discussion --- p.139 / Chapter Chapter 4 --- Summary and Finial Conslusion --- p.142 / References --- p.144

Cathelicidins are cationic host defence peptides (CHDP) with essential roles in the innate defence system. These peptides have antimicrobial potential and the capacity to modulate innate immunity and inflammatory processes. Neutrophils (PMN) are the main reservoir of cathelicidins and play key roles in first line defence against infection. The appropriate regulation of PMN function, death, and clearance is critical to innate immunity, and the efferocytosis of apoptotic PMN, in contrast to necrotic cells, is proposed to promote the resolution of inflammation. In this thesis I demonstrate that the human cathelicidin LL-37 rapidly induced secondary necrosis of apoptotic human PMN and identify the essential C-terminal region of LL-37 required for this activity. In addition to the induction of secondary necrosis, higher concentrations of LL-37 also promoted PMN granule contents release. LL-37-induced secondary necrosis did not affect PMN ingestion by human monocyte-derived macrophages and, in contrast to expectation, was not proinflammatory. Interestingly, the anti-inflammatory effects of apoptotic PMN on activated macrophages were retained and even potentiated where LL-37-mediated secondary necrosis induced anti-inflammatory granule content release. Consistent with the results of in vitro studies, in vivo murine sterile peritonitis model revealed the same phenomenon: LL-37-induced secondary necrosis diminished inflammatory responses with decreased PMN influx. I also present data on LL-37- mediated modulation of innate immune effector cell cytokines responses to inflammatory signals. I propose that during acute inflammation LL-37 can modulate innate immune responses through its activity on cytokine production, and that LL-37-mediated secondary necrosis of apoptotic PMN has anti-inflammatory effects, but may also mediate host damage by promoting the release of potentially harmful intracellular contents under chronic or dysregulated conditions.

Orientador: Daniela Leal Zandim-Barcelos / Banca: Joni Augusto Cirelli / Banca: Flávia Aparecida Chaves Furlaneto Messora / Resumo: Os peptídeos antimicrobianos são componentes da resposta imune inata, que apresentam propriedades imunomodulatórias adjuntas às propriedades antimicrobianas e, portanto, podem ter um papel chave na susceptibilidade ou resistência a doenças na cavidade oral.O propósito deste estudo foi investigar a influência do tabagismo sobre os níveis dos peptídeos antimicrobianos, alfa-defensinas (HNP 1-3) e LL-37, no fluido crevicular gengival de pacientes com periodontite crônica, e avaliar a relação destes peptídeos com saúde e doença periodontal. Um total de 40 pacientes com periodontite crônica, sendo 20 fumantes e 20 não fumantes, e 20 pacientes periodontalmente saudáveis foram incluídos no estudo. Os parâmetros clínicos avaliados foram: profundidade de sondagem, sangramento à sondagem, nível clínico de inserção, Índice de placa visível e Índice de sangramento gengival. Amostras de fluido crevicular gengival foram coletadas com tiras de papel absorvente e o volume mensurado com Periotron. Nos pacientes com periodontite crônica, foram coletadas amostras de sítios sadios e doentes. A quantificação da LL-37 e HNP 1-3 foi realizada pela técnica ELISA sanduíche.Os níveis de LL-37 e HNP 1-3 foram menores tanto nos sítios sadios como nos sítios doentes de pacientes fumantes em comparação com os não fumantes, sendo essas diferenças significativas exceto para os níveis de LL-37 nos sítios sadios (p<0,05). Os sítios doentes dos pacientes fumantes e não fumantes com periodontite crônica mostrar... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Antimicrobial peptides are components of the innate immune response that have immunomodulatory properties adjuncts to the antimicrobial properties and, therefore, may have a key role in susceptibility or resistance to diseases in the oral cavity. The purpose of this study was to investigate the influence of smoking on the levels of antimicrobial peptides, alpha-defensins (HNP 1-3) and LL-37 in the gingival crevicular fluid of patients with chronic periodontitis, and evaluate the relationship of these peptides with health and periodontal disease. A total of 40 patients with chronic periodontitis, 20 smokers and 20 non-smokers, and 20 periodontally healthy patients were included in the study. The clinical parameters evaluated were probing depth, bleeding on probing, clinical attachment level, visible plaque index and gingival bleeding index. Samples of gingival crevicular fluid were collected with absorbent paper strips and the volume measured on Periotron. In patients with chronic periodontitis, samples of healthy and diseased sites were collected. The quantification of LL-37 and HNP 1-3 was carried out by sandwich ELISA tecnique. The levels of LL-37 and HNP 1-3 were lower both in healthy sites such as diseased sites in smokers compared to non-smokers, those with significant differences except for the LL-37 levels in healthy sites (p<0.05). Diseased sites of smokers and non-smokers with chronic periodontitis patients showed higher levels of LL-37 and lower levels of HNP 1-3 th... (Complete abstract click electronic access below) / Mestre

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Os peptídeos antimicrobianos desempenham papéis protetores críticos em uma gama de doenças humanas, incluindo o câncer. Vários estudos demonstraram funções - tais como proliferação, angiogênese, apoptose e imunomodulação - desses peptídeos em vias cancerígenas cruciais. Investigamos o papel do Peptídeo antimicrobiano LL-37 sobre stemness em câncer de mama (SKBR3) e células de melanoma (A375). Análise por PCR array da expressão diferencial de genes em SKBR3 e A375 com knockdown por siRNA para o mRNA de LL-37 revelou uma regulação negativa de genes relacionados com stemness, incluindo transcriptase reversa da telomerase, forkhead box D3 e para o fator indiferenciado de transcrição de células embrionárias 1, notavelmente em células de câncer de mama.Além disso, as células SKBR3 com knockdown para a expressão de LL-37 mostraram uma diminuição da produção de oncosferas em comparação com controles negativos, enquanto as células A375 exibiram uma produção aumentada. Tomados em conjunto, nossos achados indicam um papel para LL- 37 em stemness, dependendo do tipo de celular analisado / Antimicrobial peptides play critical protective roles in a range of human diseases, including cancer. Multiple studies have demonstrated functions -- such as proliferation, angiogenesis, apoptosis and immunomodulation -- of these peptides in crucial cancer pathways. We investigated the role of the antimicrobial peptide LL-37 on stemness in breast cancer (SKBR3) and melanoma cells (A375). PCR array analysis of differential gene expression in SKBR3 and A375 cancer cell lines downregulated for LL-37 expression by siRNA revealed downregulation of genes related to stemness, including telomerase reverse transcriptase, forkhead box D3 and undifferentiated embryonic cell transcription factor 1, remarkably in breast cancer cells. Furthermore, SKBR3 cells knocked down for LL-37 expression showed a decreased production of oncospheres in comparison with negative controls, while A375 cells exhibited increased production. Taken collectively, our findings indicate a role for LL-37 in cancer cell stemness depending on the cell type

Os peptídeos antimicrobianos desempenham papéis protetores críticos em uma gama de doenças humanas, incluindo o câncer. Vários estudos demonstraram funções - tais como proliferação, angiogênese, apoptose e imunomodulação - desses peptídeos em vias cancerígenas cruciais. Investigamos o papel do Peptídeo antimicrobiano LL-37 sobre stemness em câncer de mama (SKBR3) e células de melanoma (A375). Análise por PCR array da expressão diferencial de genes em SKBR3 e A375 com knockdown por siRNA para o mRNA de LL-37 revelou uma regulação negativa de genes relacionados com stemness, incluindo transcriptase reversa da telomerase, forkhead box D3 e para o fator indiferenciado de transcrição de células embrionárias 1, notavelmente em células de câncer de mama.Além disso, as células SKBR3 com knockdown para a expressão de LL-37 mostraram uma diminuição da produção de oncosferas em comparação com controles negativos, enquanto as células A375 exibiram uma produção aumentada. Tomados em conjunto, nossos achados indicam um papel para LL- 37 em stemness, dependendo do tipo de celular analisado / Antimicrobial peptides play critical protective roles in a range of human diseases, including cancer. Multiple studies have demonstrated functions -- such as proliferation, angiogenesis, apoptosis and immunomodulation -- of these peptides in crucial cancer pathways. We investigated the role of the antimicrobial peptide LL-37 on stemness in breast cancer (SKBR3) and melanoma cells (A375). PCR array analysis of differential gene expression in SKBR3 and A375 cancer cell lines downregulated for LL-37 expression by siRNA revealed downregulation of genes related to stemness, including telomerase reverse transcriptase, forkhead box D3 and undifferentiated embryonic cell transcription factor 1, remarkably in breast cancer cells. Furthermore, SKBR3 cells knocked down for LL-37 expression showed a decreased production of oncospheres in comparison with negative controls, while A375 cells exhibited increased production. Taken collectively, our findings indicate a role for LL-37 in cancer cell stemness depending on the cell type