High-grade serous ovarian carcinoma (HGSOC) is the most frequent type of ovarian cancer and has a poor outcome. It has been proposed that fallopian tube cancers may be precursors of HGSOC but evolutionary evidence for this hypothesis has been limited. Here, we perform whole-exome sequence and copy number analyses of laser capture microdissected fallopian tube lesions (p53 signatures, serous tubal intraepithelial carcinomas (STICs), and fallopian tube carcinomas), ovarian cancers, and metastases from nine patients. The majority of tumor-specific alterations in ovarian cancers were present in STICs, including those affecting TP53, BRCA1, BRCA2 or PTEN. Evolutionary analyses reveal that p53 signatures and STICs are precursors of ovarian carcinoma and identify a window of 7 years between development of a STIC and initiation of ovarian carcinoma, with metastases following rapidly thereafter. Our results provide insights into the etiology of ovarian cancer and have implications for prevention, early detection and therapeutic intervention of this disease.

The p53 homologue p63 encodes for different isotypes able to either transactivate p53 reporter genes (TAp63) or act as p53-dominant-negatives (DeltaNp63). p63 is expressed in the basal cells of many epithelial organs and its germline inactivation in the mouse results in agenesis of organs such as skin appendages and the breast. Here, we show that prostate basal cells, but not secretory or neuroendocrine cells, express p63. In addition, prostate basal cells in culture predominantly express the DeltaNp63alpha isotype. In contrast, p63 protein is not detected in human prostate adenocarcinomas. Finally, and most importantly, p63(-/-) mice do not develop the prostate. These results indicate that p63 is required for prostate development and support the hypothesis that basal cells represent and/or include prostate stem cells. Furthermore, our results show that p63 immunohistochemistry may be a valuable tool in the differential diagnosis of benign versus malignant prostatic lesions.

Growth factor-dependent accumulation of the cyclin D1 proto-oncogene is balanced by its rapid phosphorylation-dependent proteolysis. Degradation is triggered by threonine 286 phosphorylation, which promotes its ubiquitination by an unknown E3 ligase. We demonstrate that Thr286-phosphorylated cyclin D1 is recognized by a Skp1-Cul1-F box (SCF) ubiquitin ligase where FBX4 and alphaB crystallin govern substrate specificity. Overexpression of FBX4 and alphaB crystallin triggered cyclin D1 ubiquitination and increased cyclin D1 turnover. Impairment of SCF(FBX4-alphaB crystallin) function attenuated cyclin D1 ubiquitination, promoting cyclin D1 overexpression and accelerated cell-cycle progression. Purified SCF(FBX4-alphaB crystallin) catalyzed polyubiquitination of cyclin D1 in vitro. Consistent with a putative role for a cyclin D1 E3 ligase in tumorigenesis, FBX4 and alphaB crystallin expression was reduced in tumor-derived cell lines and a subset of primary human cancers that overexpress cyclin D1. We conclude that SCF(FBX4-alphaB crystallin) is an E3 ubiquitin ligase that promotes ubiquitin-dependent degradation of Thr286-phosphorylated cyclin D1.

Summary SCFFbx4 was recently identified as the E3 ligase for cyclin D1. We now describe cell cycle-dependent phosphorylation and dimerization of Fbx4 that is regulated by GSK3β and defective in human cancer. We present data demonstrating that a pathway involving Ras-Akt-GSK3β controls the temporal phosphorylation and dimerization of the SCFFbx4 E3 ligase. Inhibition of Fbx4 activity results in accumulation of nuclear cyclin D1 and oncogenic transformation. The importance of this regulatory pathway for normal cell growth is emphasized by the prevalence of mutations in Fbx4 in human cancer that impair dimerization. Collectively, this data reveals that inactivation of the cyclin D1 E3 ligase will likely contribute to cyclin D1 overexpression in a significant fraction of human cancer.

Deregulation of cyclin D1 occurs in numerous human cancers through mutations, alternative splicing, and gene amplification. Although cancer-derived cyclin D1 mutants are potent oncogenes in vitro and in vivo, the mechanisms whereby they contribute to neoplasia are poorly understood. We now provide evidence derived from both mouse models and human cancer-derived cells revealing that nuclear accumulation of catalytically active mutant cyclin D1/CDK4 complexes triggers DNA rereplication, resulting from Cdt1 stabilization, which in turn triggers the DNA damage checkpoint and p53-dependent apoptosis. Loss of p53 through mutations or targeted deletion results in increased genomic instability and neoplastic growth. Collectively, the data presented reveal mechanistic insights into how uncoupling of critical cell cycle regulatory events will perturb DNA replication fidelity, thereby contributing to neoplastic transformation.[Keywords: Cdt1; Cul4; cyclin D1T286A; cyclin D1P287A; rereplication; p53; genomic instability] Supplemental material is available at http://www.genesdev.org. Received June 22, 2007; revised version accepted September 21, 2007. Dysregulation of the pathways that contribute to the normal integration of growth factor signaling and cell division lies at the heart of neoplastic growth. Cyclin D expression, accumulation, and its ability to associate with catalytic partners CDK4/6 are regulated by mitogenic signaling, allowing D cyclins to serve as mediators of growth factor signaling and cell cycle progression (Gladden and Diehl 2005). Cyclin D1 gene expression depends on activation of the small GTP-binding protein, Ras (Marshall 1999). Ras activates canonical MAP kinase signaling (RAF-MEK-ERK); activation of this pathway is both necessary and sufficient for cyclin D1 expression and association with CDK4 (Albanese et al. 1995;Lavoie et al. 1996;Aktas et al. 1997;Cheng et al. 1998). Ras also contributes to the accumulation of the cyclin D1 protein, via a pathway involving PI3K and Akt, which attenuates the GSK3␤ kinase (Franke et al. 1995(Franke et al. , 1997; GSK3␤-dependent phosphorylation of cyclin D1 on Thr286 promotes cyclin D1 proteolysis (Diehl et al. 1998). Cyclin D1 subcellular localization is also regulated during cell cycle progression. Phosphorylation of cyclin D1 on Thr286 at the G1/S-phase boundary promotes CRM1-dependent nuclear export (Alt et al. 2000). Thus, Thr286 phosphorylation coordinates two critical regulatory events. First, it removes the cyclin D1 kinase from the nucleus during S phase, thereby sequestering it from potential substrates. Second, ubiquitin-mediated destruction of cyclin D1 requires cytoplasmic localization, as the D1 E3 ligase is restricted to the cytoplasm (Lin et al. 2006).Cyclin D1 overexpression occurs in carcinomas of the esophagus, head and neck, breast, and colon, as well as certain B-cell lymphomas (Bartkova et al. 1994a(Bartkova et al. ,b, 1995Gillett et al. 1994;Herman et al. 1995;Barnes and Gillett 1998;Hibberts et al. 1999;Hosokawa et al. 1999; BaniHani...

ARIEL2 (NCT01891344) is a single-arm, open-label phase 2 study of the PARP inhibitor (PARPi) rucaparib in relapsed high-grade ovarian carcinoma. In this post hoc exploratory biomarker analysis of pre- and post-platinum ARIEL2 samples, RAD51C and RAD51D mutations and high-level BRCA1 promoter methylation predict response to rucaparib, similar to BRCA1/BRCA2 mutations. BRCA1 methylation loss may be a major cross-resistance mechanism to platinum and PARPi. Genomic scars associated with homologous recombination deficiency are irreversible, persisting even as platinum resistance develops, and therefore are predictive of rucaparib response only in platinum-sensitive disease. The RAS, AKT, and cell cycle pathways may be additional modulators of PARPi sensitivity.

PrEC represents an epithelial population whose basal characteristics are modified in response to matrigel, stromal factors, and senescence, consistent with a transient amplifying population. These cells may derive from a previously unrecognized, involucrin-positive subset present in vivo.

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