TGFβ Signaling Promotes Juvenile Granulosa Cell Tumorigenesis by Suppressing Apoptosis

Abstract

Molecular changes that give rise to granulosa cell tumors of the ovary are not well understood. Previously, we showed that deletion in granulosa cells of the bone morphogenetic protein receptor-signaling transcription factors, Smad1 and Smad5, causes development of metastatic granulosa cell tumors that phenocopy the juvenile form of granulosa cell tumors (JGCTs) in humans. The TGFβ-SMAD2/3 pathway is active in JGCTs, but its role is unknown. We tested the in vivo contribution of TGFβ-SMAD signaling to JGCT development by genetically deleting the common Smad4 from Smad1/5 double knockout mice. Smad1/5/4 triple knockout mice were sterile and had significantly increased survival and delayed tumor development compared to those for the Smad1/5 double knockout mice. The few tumors that did develop were smaller, showed no evidence of metastasis, and had increased apoptosis. In the human JGCT cell line COV434, TGFβ1 increased viability by inhibiting apoptosis through a TGFβ type I receptor-dependent repression of caspase activity and inhibition of poly(ADP-ribose) polymerase cleavage. These data support a tumor-promoting function of TGFβ in JGCTs through its ability to repress apoptosis.

SMAD3 Activation: A Converging Point of Dysregulated TGF-Beta Superfamily Signaling and Genetic Aberrations in Granulosa Cell Tumor Development?

“…Because canonical BMP signaling activity is attenuated in Smad1/5 conditional knockout mice, disruption of the Smad4 gene in this model is expected to further block SMAD4-dependent TGFB/activin signaling. It is interesting to note that tumors developed in Smad1/5/4 triple conditional knockout mice are not metastatic but are prone to apoptosis [41]. These findings support that TGFB signaling promotes the proliferation of granulosa cells [42–44].…”

“…Interestingly, ovaries from Smad1/5 and Bmpr1a/Bmpr1b conditional knockout mice express high levels of TGFB downstream target genes such as TGFB induced ( Tgfbi ) and matrix metallopeptidase 2 ( Mmp2 ) and/or harbor SMAD2/3 activation, in concordance with the antagonism between TGFB and BMP signaling pathways [10, 11, 39, 40]. Generation of Smad1/5/4 triple conditional knockout mice by the Pangas laboratory further indicates that SMAD4-dependent TGFB/activin signaling may be tumorigenic in the mouse ovary [41]. Because canonical BMP signaling activity is attenuated in Smad1/5 conditional knockout mice, disruption of the Smad4 gene in this model is expected to further block SMAD4-dependent TGFB/activin signaling.…”

“…Although limited information on transcriptomic changes of human GCTs is available in publicly available databases including GEO DataSets, Oncomine, Cbioportal, and The Cancer Genome Atlas, partially due to the rarity of this type of tumors in women, emerging evidence indicates that TGFB/activin signaling is active in human GCTs [12, 31, 41]. Currently, there are only two established GCT cell lines available in this research field.…”

Follistatin is critical for mouse uterine receptivity and decidualization

“…Antagonism between signaling by the TGFβ/activin and BMP families of ligands has been reported in numerous developmental processes (30)(31)(32) and tissues (33)(34)(35)(36)(37)(38). Dysregulation of this antagonism can have dramatic consequences for tissue homeostasis, as seen in juvenile granulosa cell tumors, in which mouse models have shown that tumorigenesis is promoted by TGFβ/activin signaling through SMAD2/3 and is opposed by BMP signaling through SMAD1/5 (39)(40)(41)(42)(43)(44)(45)(46)(47). Direct competition between the pathways can occur for availability of the shared type 2 receptors ACVR2A/B (48)(49)(50) or the availability of the common cofactor SMAD4 (51).…”

FOXO1/3 and PTEN Depletion in Granulosa Cells Promotes Ovarian Granulosa Cell Tumor Development

“…Recent molecular and immunohistochemical (IHC) analyses of AGCTs indicate that FOXL2 is a central transcription factor in the ovary and that with GATA4 and phosphorylated SMAD2/3 (pSMAD2/3) are likely key players in tumor growth (26 -28, 33, 34). Mouse models that develop GCTs have been generated (10,31,(35)(36)(37)(38)(39)(40) and have provided important clues about factors controlling GCT formation. In particular, the wingless type mouse mammary tumor virus integration site family (WNT)/␤-catenin and TGF␤/activin/SMAD pathways appear to be factors involved in GCT formation (10,(37)(38)(39)(40), although none of the current mouse models completely recapitulate the molecular phenotype of AGCTs in women.…”