Hop/STI1 modulates retinal proliferation and cell death independent of PrPC.

Hop/STI1 is a co-chaperone adaptor protein for Hsp70/Hsp90 complexes. Hop/STI1 is found extracellularly and modulates cell death and differentiation through interaction with the prion protein (PrP(C)). Here, we investigated the expression of hop/STI1 and its role upon cell proliferation and cell death in the developing retina. Hop/STI1 is more expressed in developing rat retina than in the mature tissue. Hop/STI1 blocks retinal cell death in the neuroblastic layer (NBL) in a PrP(C) dependent manner, but failed to protect ganglion cells against axotomy-induced cell death. An antibody raised against hop/STI1 (alpha-STI1) blocked both ganglion cell and NBL cell death independent of PrP(C). ERK, PI3K and signaling pathways were not involved in these effects. Hop/STI1 treatment reduced proliferation, while alpha-STI1 increased proliferation in the developing retina, both independent of PrP(C). We conclude that hop/STI1 can modulate both proliferation and cell death in the developing retina independent of PrP(C).

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