The RNA-binding protein Pumilio-2 has roles in the regulation of proliferation and innate immunity of human KGN granulosa tumor cells

The RNA-binding protein Pumilio-2 (PUM2), encoded by PUM2, is known as a translational repressor with important roles during embryonic development, cell differentiation and synapse function. Information of its roles in the ovary were sparse, yet data bank mining followed by immunohistochemistry revealed expression in nonhuman primate ovarian granulosa cells (GCs). Expression was also found in human IVF-derived GCs, in samples of human GC tumors (GCT), and in KGN cells, a well-established GCT-derived cell line. KGN cells were used to explore the roles of PUM2. A small interfering RNA (siRNA) targeting PUM2 reduced PUM2 levels in KGN cells, as seen in a proteomic analysis, which also revealed that a total of 51 proteins were lower, and the abundance of 66 proteins were increased. GO term analyses showed that the pathways mainly decreased were ‘response to virus’, ‘defence response to virus’, and ‘innate immune response’. PUM2 may thus be a regulator of the innate immune abilities of GCs. The pathway increased most was ‘cell division’, a result in line with increased proliferation of siRNA transfected KGN cells. This underlies the increased ability to close the gap in scratch assays, as individual cell velocity or directionality of migration were comparable to controls. Down-regulation of PUM2 also impaired the steroidogenic potential of KGN cells (lower HSD3B2 levels, lower progesterone in supernatant). Taken together, the results indicate fundamental roles of PUM2 not only in in the regulation of proliferation and steroidogenesis of human granulosa cells, but also in regulation of their innate immune abilites.