Filamin A in the human ovary: roles in follicle maturation and in granulosa cell tumors

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Filamin A (FLNA) is an X-chromosomal encoded, well-characterized cytoskeletal protein. FLNA cross-links actin filaments and acts as an intracellular signaling scaffold by binding to a multitude of structural and signaling network components. Thereby it regulates cell shape and fate, as well as migration during development and morphogenesis. FLNA has emerging roles in tumor biology. Expression and roles of FLNA in the mammalian gonads are largely unknown. We recently described FLNA in the human testis, testicular tumors and a seminoma cell line. The studies, in which we also employed CRISPR/Cas9-mediated knockouts, confirmed an essential involvement of FLNA in regulation of the cellular phenotype and cell migration. The absence of information on FLNA in the female gonad, the most dynamic organ of the adult hosting multiple morphogenic events, led us to search data bases and to perform pilot studies. It became apparent that FLNA is expressed by human granulosa cells (GCs), and increases strikingly in growing follicles up to ovulation. Cultured human IVF-derived GCs, stemming from pre-ovulatory follicles, express FLNA in vitro, and a pilot immunoprecipitation/mass spectrometry study indicated steroidogenic enzymes and gap junction proteins as potential, novel FLNA-interaction partners, next to actin and cytoskeletal proteins. FLNA was also found in granulosa cell tumors (GCTs), which are derived from human GCs, and in KGN cells, a widely studied GCT cell line. Preliminary studies in KGN cells, in which FLNA was deleted (CRISPR/Cas9) indicated massively altered biomechanical properties and increased cell growth. Based on these results we put forward the hypothesis (1) that FLNA is a previously unexplored, highly regulated factor with important roles in the growing human follicle and the ovulatory process. In addition, the preliminary data prompts us to also hypothesize (2) that FLNA may play a role in the growth and progression of GCTs and may serve as a biomarker. We will study expression in the ovary and use primary human GCs and KGN cells to decipher regulation, function and interaction partners of FLNA in ovarian cells. To this end we will employ immunoprecipitation/mass spectrometry studies. We will examine the role of FLNA for morphology, cell proliferation and biomechanical properties using KGN cells, in which FLNA is deleted. Further, investigations in primary GCTs, including a tissue microarray (TMA), will address the question, whether FLNA may serve as a biomarker for GCTs. Studies in non-human primate ovaries are possible via an international collaboration and the availability of rodent ovaries include the possibility to investigate FLNA knockout mice. We expect novel translational data on the role of ovarian FLNA in health and disease.