BACKGROUND: P53 is a tumor suppressor protein that acts to regulate the cell cycle and, therefore, regulate cell division processes and cell death processes. P53 mutations are classified as either contact mutations, where changes are found in the residues that contact with DNA, or structural mutations, where changes cause either a full or partial distortion of the conformation. Certain “hotspot” mutations have been identified, and these abolish the functionality of p53 as a tumor suppressor. P53’s function as a tumor suppressor is two-fold. It induces cellular apoptosis and affects the cell cycle. The DREAM complex (dimerization partner, RB-like, E2F and multi-vulval Class B complex) works by repression of gene expression or activation of gene expression. Indirectly, p53 activates this DREAM complex to repress cell cycle genes by replacing the activating complex. Human pituitary adenomas, the second most common intracranial tumors, usually form from different cell types in the anterior pituitary. If these adenomas secrete a pituitary hormone (GH, PRL, ACTH, or TSH), they are termed clinically functioning. If not, they are deemed clinically nonfunctioning. Pituitary tumors have a diverse genetic background, which include germline genetic defects, tumor genetic defects, and somatic genetic changes. Human pituitary carcinomas are much more rare than pituitary adenomas, and they are only usually diagnosed due to the pituitary tumor being noncontiguous with the sella turcica region and/or metastasis of the pituitary tumor. Because of the rarity of these, the genetics of these tumors is not well-documented, and the plan of treatment is diverse. In particular, corticotropic tumors are pituitary adenomas or pituitary carcinomas that are either clinically functioning, which secrete adrenocorticotropin (ACTH), or silent, which do not secrete ACTH. If the tumor is functioning, many patients have symptoms of Cushing’s disease (CD) due to the hypersecretion of ACTH, which triggers an increase in hormone production downstream hormone production.
OBJECTIVE: This thesis seeks to describe a cohort of patients with functional corticotropic tumors and patients with silent (nonfunctioning) corticotropic tumors. In this cohort of patients, this thesis strives to find the gene mutations in this cohort to find a correlation between TP53 gene mutations that would affect the functionality of the p53 protein and the formation of corticotropic adenomas.
METHODS: A total of 38 tumor samples from 36 patients between the ages of 20 and 79 were studied for somatic mutations. By way of whole-exome sequencing with normal DNA pairs, somatic mutations for each of the samples were determined. Along with somatic mutations, some samples were sequenced for germline mutations. RNA sequencing was completed to find somatic mutations and check the gene expression and gene transcription to compare to the somatic mutations found by way of whole-exome sequencing. Each of the somatic mutations found for TP53 were verified by ClinVar and COSMIC databases.
RESULTS: From whole-exome sequencing, three samples out of the 38 samples were found to contain somatic mutations in the TP53 gene. In sample 29, two missense somatic mutations were found. First, in codon 743 (c.943G>A), this mutation produced the variant p53 protein, R248Q, a “hotspot” mutation. Second, in codon 523 (c.523C>T), this mutation produced the variant p53 protein, R175C. In sample 30, a missense mutation was found in codon 641 (c.641A>G), which produced the variant p53 protein, H214R. Last, in sample 36, a splice donor mutation was found in nucleotide 993 (c.993+1G>A), the variant located on intron 9 altered the consensus splice donor site. This resulted in an inclusion on intron 9 between exon 9 and exon 10, which produces a disrupted p53 protein.
CONCLUSION: No patients with Cushing’s disease were found to have TP53 mutations, and 3 out of the 14 patients classified as silent corticotrophs had somatic mutations in the TP53 gene. Due to finding three patients that have a somatic mutation in the TP53 gene, and that, in each of these cases, the pituitary adenomas are all silent and aggressive, we can conclude that there is a correlation between TP53 gene mutations that produce an ineffective p53 protein and the formation of aggressive corticotropic adenomas.
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/43453 |
| Date | 23 November 2021 |
| Creators | Macdonald, Kyle |
| Contributors | McKnight, C. James |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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