Abstract The luteinizing hormone receptor (LHR) is a G protein-coupled receptor (GPCR) that has a large N-terminal ligand binding ectodomain. The LHR ectodomain splice variant, expressed concomitantly with the full-length LHR in tissues, has an unknown biological function. GPCRs are a major pharmacological target, however, very little is known about the intracellular regulation of these receptors. In the present work, expression and maturation of the rat LHR and its variant were elucidated using both tissues and heterologous expression systems. A special effort was made to identify the role of developmental stage and tissue type on the LHR maturation and to find out about the molecular role of the ectodomain splice variant. We found two sites of localization for the receptor, namely the sensory system and urogenital tissues. This was demonstrated at mRNA and protein level and by rat LHR promoter-driven β-galactosidase (β-Gal) expression in the mice. In neurons, the β-Gal co-localized with the cytochrome P450 side chain cleavage enzyme, which may indicate a novel role in the neurosteroid synthesis. The neuronal LHR was expressed in the mature and immature protein forms in both developing and adult tissues, being able to bind hormone with similar high-affinity as gonadal receptors. In contrast, only immature receptors were detected in the fetal rat urogenital structures. A significant novel finding was substantial upregulation of the LHR in pregnant female rat adrenal glands and kidneys at a time that coincides with the differentiation of the fetal urogenital tissues. The mice overexpressing the ectodomain splice variant showed interference in pituitary-gonadal functions and morphological changes in the urogenital tissues. The studies showed that the variant was an endoplasmic reticulum (ER)-retained soluble protein. It accumulated in juxtanuclear regions of the ER together with ER folding chaperones and was a substrate for ER associated degradation (ERAD). The co-expression of the variant with the full-length receptor decreased the amount of receptors and misrouted them to the juxtanuclear ER subcompartment. Taken together, we suggest that the maturation of the LHR protein is developmentally and physiologically regulated at the post-translational level in tissues. The LHR ectodomain splice variant possibly modulates post-translationally the number of full-length receptors through physiological signals. Our observation of the chaperone and protein accumulation into a specific ER subcompartment may represent a protein quality control holding compartment for inefficiently/misfolded ERAD substrates.

Aberrant androgen receptor (AR) activity plays a critical role in the development and progression of both early-staged organ-confined and late-staged metastatic human prostate cancer. Recent large-scale genomic sequencing studies showed that ~50% of organ-confined prostate cancer patients have genetic rearrangements that placed the ETS transcription factors (e.g. ERG, ETV1) under the control of androgen-regulated gene promoters such as TMPRSS2. This results in the upregulation of the ETS transcription factors’ expressions in the presence of androgens. The aberrant overexpression of the ETS transcription factors are shown to induce the expression of genes that promote the cellular motility and invasive potential of prostate-tumor cells. Moreover, the improved therapeutic outcome of the second-generation anti-androgen therapies (e.g. abiraterone and enzalutamide) are encouraging, and prove that aberrant AR activity still drives the progression of metastatic prostate cancer. Although these treatments are initially effective, these cancer cells eventually develop resistance to these AR-targeted therapies termed castration-resistant prostate cancer (CRPC). Since the molecular steps involved in AR activation is still not clearly defined, it is critical to define the interactions required for AR activation prostate cancer cells, which will provide a framework for establishing more effective treatments to inhibit aberrant AR activity in human prostate cancer cells. Here, I developed a cellular system to isolate ligand-dependent interactions of AR in prostate-tumor cells. A siRNA luciferase screen was also developed and identified novel modulators of AR-mediated transcription selected from the proteomic dataset. Further biochemical studies showed that AR is associated with the Golgi membrane in a ligand-sensitive manner. And that the nuclear localization of ARA160, an AR coactivator, is regulated by the COPI retrograde trafficking machinery. Collectively, these results support the use of this cellular system to decipher the known AR-interacting proteins and novel components involved in AR signaling in prostate-tumor cells. I next investigated the androgen-sensitive AR transcriptional complexes and androgen-sensitive microsomes isolated from LNCaP prostate-tumor cells. Both studies yielded results that would further strengthen the diverse AR actions mediated within the cell. These results further support the notion that there is significant crosstalk amongst different cell surface receptor signaling pathways with AR. An extension of the androgen-sensitive microsome findings also led us to study the androgen-sensitive G-protein coupled receptor, CXCR7. I showed that androgens regulate the expressions of CXCR7 and CXCR4 and in turn modulated CXCL12-mediated motility in prostate tumor cells. Lastly, biochemical strategies were developed to detect differences in glycoprotein expression of frozen prostate cancer tissues isolated from human patients. I showed that the workflow successfully solubilized and isolated N- and O-linked glycoproteins from the frozen tissue samples and can be analyzed by quantitative mass spectrometry. This workflow would thus facilitate future biomarker studies. In summary, these data demonstrate the utility of developing methods for the comprehensive mapping of AR-mediated signaling in prostate cancer cells, and thus provide novel target candidates for the therapeutic treatment of metastatic or CRPC.

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One of the oldest, extant, lineages of vertebrates, the sea lamprey, was used to clarify the evolutionary origin and divergence of the growth hormone receptor (GHR) family. A single, full-length, cDNA, and a second, partial, cDNA were identified and shown to encode proteins that share amino acid identity with GHRs and prolactin receptors (PRLR s) previously identified. The complexity of the dynamic signaling system, with special emphasis on this system in fish and in the context of the evolution of this system, is discussed in the first chapter. The second chapter integrates the new insights gained by these studies. Included is a newly proposed phylogenetic analysis and revised nomenclature-system for vertebrate GHRs that better represents the evolutionary history of the receptor family. The molecular evolution of the receptors is, furthermore, highlighted as the backdrop for the continued discussion regarding how the GH-family of hormones exhibit such coordinated and pleiotropic actions.

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La sequía y la salinidad representan estreses ambientales que afectan de forma crítica el crecimiento de las plantas y limitan enormemente su potencial agrícola. La fitohormona ácido abcísico (ABA) juega un papel fundamental en la coordinación de la respuesta y adaptación de las plantas a este tipo de estreses, así como en la regulación del crecimiento y desarrollo vegetal. Elementos intermediarios de la ruta de señalización ya habían sido caracterizados, pero aún se desconocía el mecanismo de percepción y transducción de señal de la hormona. Este trabajo de tesis ha contribuido a la caracterización de una nueva familia de receptores intracelulares de la hormona ABA, formada por 14 miembros y denominada PYR/PYL (de pyrabactin resistance / PYR1-like) /RCAR (de Regulatory Component of Abscisic acid Receptor), y a su caracterización estructural y bioquímica. Estas proteínas son capaces de unir de forma específica la hormona ABA. La unión de la hormona induce en estos receptores un cambio conformacional, que les permite regular la actividad de los reguladores negativos de la ruta: fosfatasas del grupo A como ABI1, ABI2 o HAB1 ( Leung et al., 1994; Meyer et al.,1994; Saez et al., 2004). Para la caracterización de estos receptores se han llevado a cabo abordajes genéticos, bioquímicos, de calorimetría y estudios estructurales. / Santiago Cuéllar, J. (2011). Structural insights into ABA perception and signalling: structure of ABA receptor PYR1 [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/13260