Retinoic acid- and phorbol ester-induced neuronal differentiation down-regulates caveolin expression in GnRH neurons

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GN11 and GT1-7 are immortalized gonadotropin-releasing hormone-positive murine cell lines exhibiting the features of immature olfactory neurons and differentiated hypothalamic neurons, respectively. Using electron microscopy and biochemical assays (RT-PCR and immunoblotting) we determined the presence of numerous caveolae invaginations and of caveolin-1 and −2 mRNAs and proteins in GN11 cells, and their absence in GT1-7 cells. The lack of caveolins in GT1-7 cells might be due to the silencing of gene transcription caused by estrogen receptor α whose inhibitory activity in GN11 cells could be counter-balanced by co-expression of caveolin-permissive estrogen receptor β. To test whether the unique expression of caveolins in GN11 cells is related to their immature state, we treated GN11 cells for 24–72 h with retinoic acid or phorbol ester. Both treatments led to neuronal differentiation of GN11 cells, as shown by emission of long neuritic processes, increased expression of growth cone-associated protein-43 and appearance of voltage-gated K+ and Ca2+ channel currents. Concurrently, caveolins 1 and 2, and estrogen receptor β were down-regulated in differentiated GN11, whereas estrogen receptor α was unaffected by differentiation. We conclude that caveolin expression in GN11 neurons is down-regulated upon differentiation and up-regulated by estrogen receptor β.

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