Carcinoma initiation via RB tumor suppressor inactivation: a versatile approach to epithelial subtype-dependent cancer initiation in diverse tissues

Inactivation of TRP53, PTEN, RB1, and/or CDH1 in the ovarian surface epithelium induces ovarian cancer transformation and metastasis

Ovarian cancer (OvCa) remains the most common cause of death from gynecological malignancies. Genetically engineered mouse models have been used to study initiation, origin, progression, and/or mechanisms of OvCa. Based on the clinical features of OvCa, we examined a quadruple combination of pathway perturbations including PTEN, TRP53, RB1, and/or CDH1. To characterize the cancer-promoting events in the ovarian surface epithelium (OSE), Amhr2cre/+ mice were used to ablate floxed alleles of Pten, Trp53, and Cdh1, which were crossed with TgK19GT121 mice to inactivate RB1 in KRT19-expressing cells. Inactivation of PTEN, TRP53, and RB1 with or without CDH1 led to the development of type I low-grade OvCa with enlarged serous papillary carcinomas and some high-grade serous carcinomas (HGSCs) in older mice. Initiation of epithelial hyperplasia and micropapillary carcinoma started earlier at 1 month in the triple mutations of Trp53, Pten, and Rb1 mice as compared to 2 months in quadruple mutations of Trp53, Pten, Rb1, and Cdh1 mice, whereas both genotypes eventually developed enlarged proliferating tumors that invaded into the ovary at 3-4 months. Mice with triple and quadruple mutations developed HGSC and/or metastatic tumors, which disseminated into the peritoneal cavity at 4-6 months. In summary, inactivation of PTEN, TRP53, and RB1 initiates OvCa from the OSE. Additional ablation of CDH1 further increased persistence of tumor dissemination and ascites fluid accumulation enhancing peritoneal metastasis.

A Transplantable Syngeneic Allograft Mouse Model for Nongestational Choriocarcinoma of the Ovary

Nongestational choriocarcinoma is a rare malignancy in humans with poor prognosis. Naturally occurring choriocarcinoma is also rare in laboratory mice, and no genetic mouse model accurately recapitulates the features of this cancer. Here we report development of a genetically engineered mouse (GEM) model with alterations in Brca2, Trp53, and RB that develops ovarian tumors. Most of the ovarian tumors displayed histological characteristics of nongestational choriocarcinoma of the ovary (NGCO) (47%) with abundant syncytiotrophoblasts and cytotrophoblasts, positive immunolabeling for human chorionic gonadotropin, and positive periodic acid-Schiff reaction. The rest of the ovarian tumors were serous epithelial ovarian carcinoma (SEOC) (26%) or mixed tumors consisting of NGCO and SEOC (26%). We further established syngeneic orthotopic mouse models for NGCO by in vivo passaging of GEM tumors. These metastatic models provide a platform for evaluating new treatment strategies in preclinical studies aimed at improving outcomes in choriocarcinoma patients.

Advanced Glycation End Products Increase MDM2 Expression via Transcription Factor KLF5

Type 2 diabetes increases the risk for all-site cancers including colon cancer. Diabetic patients present typical pathophysiological features including an increased level of advanced glycation end products (AGEs), which comes from a series of nonenzymatic reactions between sugars and biological macromolecules, positively associated with the occurrence of diabetic complications. MDM2 is an oncogene implicated in cancer development. The present study investigated whether diabetes promoted MDM2 expression in colon cells and the underlying mechanisms. Our results showed that AGE increased the protein level of MDM2 in a cell model and promoted binding between MDM2 and Rb as well as p53, which led to degradation of Rb and p53. KLF5 was able to bind to the regulatory sequence of the MDM2 gene, and knockdown of the KLF5 protein level inhibited the AGE-triggered MDM2 overexpression, which indicated that KLF5 was the transcription factor for MDM2. In a mouse model of diabetes, we found that AGE level was increased in serum. The protein levels of both KLF5 and MDM2 were increased. KLF5 was able to bind to the regulatory sequence of the MDM2 gene. In conclusion, our results suggest that diabetes increases the level of AGE which enhances the expression of MDM2 via transcription factor KLF5 in colon cells. MDM2 overexpression is a candidate biological link between type 2 diabetes and colon cancer development.

RB inactivation in keratin 18 positive thymic epithelial cells promotes non-cell autonomous T cell hyperproliferation in genetically engineered mice

Thymic epithelial cells (TEC), as part of thymic stroma, provide essential growth factors/cytokines and self-antigens to support T cell development and selection. Deletion of Rb family proteins in adult thymic stroma leads to T cell hyperplasia in vivo. To determine whether deletion of Rb specifically in keratin (K) 18 positive TEC was sufficient for thymocyte hyperplasia, we conditionally inactivated Rb and its family members p107 and p130 in K18+ TEC in genetically engineered mice (TgK18GT₁₂₁; K18 mice). We found that thymocyte hyperproliferation was induced in mice with Rb inactivation in K18+ TEC, while normal T cell development was maintained; suggesting that inactivation of Rb specifically in K18+ TEC was sufficient and responsible for the phenotype. Transplantation of wild type bone marrow cells into mice with Rb inactivation in K18+ TEC resulted in donor T lymphocyte hyperplasia confirming the non-cell autonomous requirement for Rb proteins in K18+ TEC in regulating T cell proliferation. Our data suggests that thymic epithelial cells play an important role in regulating lymphoid proliferation and thymus size.

Genetically engineered mouse models for epithelial ovarian cancer: are we there yet?

The development of preclinical spontaneous genetically engineered mouse models (GEMMs) requires an understanding of the genetic basis of the human disease. Such robust models have proven invaluable for increasing understanding of human malignancies as well as identifying new biomarkers and testing new therapies for these diseases. While GEMMs have been reported for ovarian cancer, the majority have proven disappointing overall in their recapitulation of paired genetic and histological features especially for serous ovarian epithelial cancer. This review describes GEMMs for ovarian cancer, in particular, high grade serous ovarian cancer and assesses these in light of recent changes in our understanding of the human malignancy.