Login to Access Video or Poster Abstract: MP65-16
Sources of Funding: NIH/NCI CA172122, BCAN Young Investigator Award

Introduction

Muscle invasive bladder cancer (MI BLCa) often consists of conventional urothelial cell carcinoma with mixed squamous cell differentiation (SqD). Presence of SqD is associated with a basal molecular subtype and poor prognosis. Previous work identified decreased expression of the transcription factor Forkhead box A1 (FOXA1) in the urothelium as a marker of SqD, and that genetic ablation of Foxa1 in the bladders of mice results in SqD. However, it is unclear how FOXA1 loss cooperates with other oncogenic changes to promote urothelial tumorigenesis and progression. Inactivation of the tumor suppressor phosphatase and tensin homolog on chromosome ten (PTEN) is associated with squamous cancers independent of anatomic site, and found in a subset of MI BLCa. Therefore, we undertook studies to identify the extent to which FOXA1 and PTEN inactivation cooperate to promote progression to MI BLCa.

Methods

We utilized the urothelial-specific uroplakin 2 promoter to drive Cre recombinase (UpII-Cre) expression, enabling us to knockout (KO) Foxa1 and/or Pten in a bladder-specific manner. Following Foxa1 and/or Pten KO, experimental mice and appropriate controls were exposed to the carcinogen N-butyl-(4-hydroxybutyl)nitrosamine (BBN) for 12, 16 and 24 weeks, followed by morphologic and immunohistochemical analyses.

Results

Similar to control mice, mice with urothelial-specific KO of one or two alleles of Foxa1 and/or Pten develop marked inflammation and proliferative hyperplasia following 12 weeks of BBN exposure, and do not develop MI BLCa until 24 weeks of exposure. However, homozygous KO of Foxa1 combined with Pten haploinsufficiency, or homozygous KO of Pten combined with Foxa1 haploinsufficency resulted in the development of carcinoma in situ and MI BLCa with squamous features following just 12 weeks of BBN exposure. In addition, MI BLCa arising in these genetically engineered mice express several markers of the basal molecular subtype, which is extremely aggressive in humans.

Conclusions

Our work indicates combined loss of Foxa1 and Pten dramatically increases sensitivity to environmental carcinogens, which is consistent with previous studies identifying an important role for these factors in BLCa. In addition, our work suggests combined FOXA1 and PTEN inactivation may be important in basal BLCa. Future studies will define the mechanism by which FOXA1 and PTEN inactivation promote tumor progression and the emergence of a basal molecular subtype of disease in the setting of carcinogen exposure.

Funding

NIH/NCI CA172122, BCAN Young Investigator Award