Either Kras activation or Pten loss similarly enhance the dominant-stable CTNNB1-induced genetic program to promote granulosa cell tumor development in the ovary and testis

WNT, PI3K or RAS signaling pathways control specific stages of ovarian follicular development. To analyze the functional interactions of these pathways in granulosa cells during follicular development in vivo, we generated specific mutant mouse models. Stable activation of the WNT signaling effector beta-catenin (CTNNB1) in granulosa cells results in the formation of premalignant lesions that develop into granulosa cell tumors (GCTs) spontaneously later in life or following targeted deletion of the tumor suppressor gene Pten. Conversely, expression of oncogenic KRAS(G12D) dramatically arrests proliferation, differentiation and apoptosis in granulosa cells, and consequently, small abnormal follicle-like structures devoid of oocytes accumulate in the ovary. Because of the potent anti-proliferative effects of KRAS(G12D) in granulosa cells, we sought to determine if KRAS(G12D) would block precancerous lesion and tumor formation in follicles of the CTNNB1 mutant mice. Unexpectedly, transgenic Ctnnb1;Kras mutant mice exhibited increased GC proliferation, decreased apoptosis and impaired differentiation and developed early-onset GCTs leading to premature death in a manner similar to the Ctnnb1;Pten mutant mice. Microarray and RT-PCR analyses revealed that gene regulatory processes induced by CTNNB1 were mostly enhanced by either KRAS activation or Pten loss in remarkably similar patterns and degree. The concomitant activation of CTNNB1 and KRAS in Sertoli cells also caused testicular granulosa cell tumors that showed gene expression patterns that partially overlapped those observed in GCTs of the ovary. Although the mutations analyzed herein have not yet been linked to adult GCTs in humans, 1) other components of these pathways may be altered or mutated, 2) these mutations may relate to juvenile GCTs or 3) they may occur in tumors of other tissues where CTNNB1 is mutated. Importantly, our results provide strong evidence that CTNNB1 is the driver in these contexts and that KRAS(G12D) and Pten loss promote the program set in motion by the CTNNB1.