Relationship Between Steroidogenic Acute Regulatory Protein Expression and Progesterone Production in Hen Granulosa Cells During Follicle Development
The present studies were conducted to address cellular mechanisms responsible for regulating steroidogenic acute regulatory protein (StAR) expression and progesterone synthesis at maturational stages corresponding to both the time of hen follicle selection, as well as before and after the LH surge i...
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Veröffentlicht in: | Biology of reproduction 2002-10, Vol.67 (4), p.1313-1320 |
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Zusammenfassung: | The present studies were conducted to address cellular mechanisms responsible for regulating steroidogenic acute regulatory
protein (StAR) expression and progesterone synthesis at maturational stages corresponding to both the time of hen follicle
selection, as well as before and after the LH surge in preovulatory follicle granulosa cells. A recently published report
has established that mitogen-activated protein (MAP) kinase signaling induced by transforming growth factor α (TGFα) treatment
blocks FSH-induced differentiation and StAR expression in cultured hen granulosa cells, whereas inhibitors of MAP kinase signaling
enhance FSH-induced differentiation. The present in vitro studies demonstrate that in addition to MAP kinase signaling, activation
of protein kinase C (PKC) blocks both FSH-induced StAR expression and the initiation of progesterone production in prehierarchal
follicle granulosa cells, whereas the pharmacologic inhibitor of PKC, GF109203X, potentiates FSH-induced StAR expression and,
as a consequence, the initiation of progesterone synthesis. Moreover, we demonstrate in granulosa cells collected from preovulatory
follicles that although an acute increase in progesterone production in response to LH treatment requires rapid transcription
and translation of StAR, the magnitude of progesterone production is rate-limited by one or more factors other than StAR (e.g.,
the P450 cholesterol side-chain enzyme). Finally, the rapid turnover of StAR protein, such as occurs following the withdrawal
of LH, provides an additional mechanism for the tight regulation of progesterone production that occurs during the hen ovulatory
cycle, and explains the rapid loss of steroidogenesis in the postovulatory follicle. In summary, data reported herein support
the proposal that paracrine/autocrine factors (including but not necessarily limited to TGFα) prevent premature expression
of StAR in prehierarchal follicle granulosa cells by more than one receptor-mediated signaling pathway. Furthermore, subsequent
to follicle selection into the preovulatory hierarchy, StAR transcription and translation is necessary but not sufficient
for the full potentiation of the preovulatory surge of serum progesterone. |
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ISSN: | 0006-3363 1529-7268 |
DOI: | 10.1095/biolreprod67.4.1313 |