Most commonly mutated genes in High Grade Serous Ovarian Carcinoma are nonessential for ovarian surface epithelial stem cell transformation

Abstract

High grade serous ovarian carcinoma (HGSOC) is the most lethal gynecological cancer and the 5 th leading cause of cancer-related deaths of women in the USA. Diseaseassociated mutations have been identified by the Cancer Genome Atlas Research Network. However, aside from mutations in TP53 or alterations in the RB1 pathway that are extremely common in HGSOC, the contributions of other mutation combinations have been difficult to assess experimentally or with genomic data alone. Previous research identified ALDH + stem cells of the ovarian surface epithelium (OSE) as one of the putative cells of HGSOC origin. Here, we performed combinatorial CRISPR mutagenesis of 20 putative HGSOC driver genes to identify mutation combinations that transformed OSE stem cells (OSE-SC) and non-stem cells (OSE-NS). Overrepresented mutations and mutation combinations were identified in all transformants and were investigated directly in targeted assays. Our results support the OSE stem cell theory of HGSOC initiation and suggest that most commonly mutated genes in HGSOC have no effect on OSE-SC transformation initiation. We suggest a model in which combined disruption of RB1 and PTEN, in addition to TP53 deficiency, constitutes a core set of mutations required for efficient transformation in vitro. A few previously uncharacterized mutation combinations further enhanced transformation but may have done so via TP53-related mechanisms. Together, our results identify mutation combinations that are critical for OSE-SC transformation and may contribute to more accurate modeling of HGSOC development. Our cancer driver screening methodology may also serve as a model for high throughput functional assessment of commonly mutated genes uncovered in other cancers by large scale sequencing.

Cancer, Retrogenes, and Evolution

“…Another example of cancer stage-specific retrocopy is SLC6A6P1 , also known as SLC6A610P , associated with recurrence in high-grade serous ovarian cancer. This subtype of ovarian cancer is very common (over 70% of affected women) [ 91 ]. Moreover, due to the lack of reliable diagnostics, it is usually detected at an advanced stage [ 87 ].…”

Cellular models of development of ovarian high‐grade serous carcinoma: A review of cell of origin and mechanisms of carcinogenesis

“…Robert et al tested 20 oncogenes postulated by TCGA and found most of them (LRP1B, FANCM, CREBBP, RAD51C, FAT3, APC, FANCD2 and GABRA6) did not improve transformation rates, whereas several (FANCD2, APC, FAT3 and RAD51C) actually reduced transformation. Only two genes, Ankrd11 and Wwox, enhanced the transformation frequency of Trp53-/Cdkn2a-/PTEN-OSE-SC 123. Deletions of both Ankrd11 and Wwox were found in genomic analysis of tumours from Trp53/Brca/PTEN-deletion mouse…”

“…The TP53/RB1disrupted cell line, FT33-shp53-R24C, was further transformed by knockdown of the B56γ subunit of protein phosphatase 2A (PP2A-B56γ)122 and c-MYC, which led to the fully transformed FT33-shp53-R24C-shPP2A-Myc cell line 105. By testing the combinations of more tumour genes, Robert et al concluded that mutations in TP53, RB1, PTEN and CDKN2A synergistically contributed to cellular transformation 123. TP53 is universally disrupted in HGSOC.Rb1 and PTEN mutations frequently coexist in multiple cancers, such as HGOSC and metastatic prostate cancer.…”

“…The four genes, Trp53, Rb1, Cdkn2a and PTEN, had the greatest conversion efficiency when targeted simultaneously. The synergistic deficiency of Trp53, Rb1 and PTEN is considered to be a core state for the efficient translation of OSE-SC in vitro 123. Robert et al tested 20 oncogenes postulated by TCGA and found most of them (LRP1B, FANCM, CREBBP, RAD51C, FAT3, APC, FANCD2 and GABRA6) did not improve transformation rates, whereas several (FANCD2, APC, FAT3 and RAD51C) actually reduced transformation.…”

Establishment of In Vivo Ovarian Cancer Mouse Models Using Intraperitoneal Tumor Cell Injection

“…Recently, The Cancer Genome Atlas Consortium (TCGA) described deregulated signaling pathways for HGSOC, which is usually classified by mutations in p53 and BRCA1/2. Also, copy number variations are more common in HGSOC than the endometrioid, clear cell, low-grade serous, and mucinous histotypes [9][10][11]. Consequently, a better understanding of key differences among various histotypes should point to targeted therapies and diagnostics to improve patient care and prognosis.…”