CCT6A, the zeta subunit of the
chaperonin containing TCP1 complex, is the only
cytosolic chaperonin in eukaryotes and is estimated to assist in the folding of multiple
proteins including actin,
tubulin,
cyclin E,
myosin,
transducin and the Von Hippel Lindau
tumor suppressor. In this study, we examined the expression of CCT6A and
progesterone receptor (PGR)
mRNA in various tissues of chickens and the regulation of CCT6A and PGR
mRNA in ovarian granulosa cells. Northern blot analysis revealed that CCT6A had one transcript and was highly expressed in the ovary tissues from chickens at both the sexually immature and mature stages. CCT6A
mRNA expression was increased maximally from pre-hierarchy follicles to F5 follicles and subsequently declined in pre-ovulatory and post-ovulatory follicles. The expression of PGR
mRNA exhibited the similar pattern to CCT6A. In granulosa cells isolated from pre-ovulatory follicles,
follicle-stimulating hormone (FSH) inhibited the expression of CCT6A
mRNA, whereas
progesterone activated CCT6A and suppressed PGR expression in a time-dependent manner. We further investigated the regulation of CCT6A transcription by
progesterone by constructing various progressive deletions and mutants and identified the core promoter
element of CCT6A and the binding region of
progesterone, which is located from -2056 to -2051. Taken together, our results indicate that CCT6A likely plays an important role in follicle growth, and in granulosa cells,
progesterone activates CCT6A transcription via a
progesterone response element (PRE) located in the distal promoter of CCT6A.