Neither the Basic Helix-Loop-Helix Transcription Factor Hand2 Nor the MAP Kinase Pathway Are Involved in Progesterone Effects on Cervical Epithelium in the Mouse.

Stroma-epithelial crosstalk is necessary for growth, regulation of proliferation and normal function of reproductive tissues. A recent study reported that the basic helix-loop-helix transcription factor Hand2 is stimulated by progesterone in uterine stroma, and is essential for progesterone-mediated inhibition of estrogen-induced epithelial proliferation in mouse uterus. Progesterone-induced inhibition of epithelial proliferation by Hand2 was mediated through suppression of members of the fibroblast growth factor family, which led to inactivation of the Erk/MAP kinase signaling pathway normally stimulated by 17β-estradiol. During the first half of pregnancy, the uterine cervix remains rigid and compact, but grows extensively during the second half, a process regulated by 17β-estradiol and progesterone. In this study, we investigated the role of Hand2 in the mouse cervix and determined whether the effects of progesterone in the cervix were dependent on this transcription factor as they are in the uterus. To evaluate whether Hand2 was involved in progesterone-mediated inhibition of cervical growth, reproductive tracts from female mice were collected on day 8 of pregnancy and from ovariectomized virgin females that received various regimens of hormone replacement. For both groups, immunohistochemistry was performed to assess expression of the following proteins: Hand2, phospho-ERK (an indication of MAP kinase activation), and MKi-67 (a marker for cell proliferation). Consistent with the previous report, Hand2 was expressed in uterine stroma during early pregnancy and in ovariectomized mice following progesterone treatment. Surprisingly, Hand2 expression in the stroma ceased abruptly and totally at the uterine-cervical junction; Hand2 was not expressed in epithelium of either organ. Similar results were seen with the ovariectomized females. Thus, Hand2 seems to be specific to the uterus, since no expression was observed in stroma at or beyond the uterine-cervical junction. Further, phospho-ERK expression was high in the cervical epithelium of ovariectomized mice treated with 17β-estradiol, and similarly high phospho-ERK expression was seen in the cervical epithelium of 17β-estradiol + progesterone treated mice. This contrasts sharply with previous results obtained in the uterus, where 17β-estradiol induces marked increases in phospho-ERK, but progesterone treatment is capable of essentially abolishing this increase. Thus, it appears that despite the anatomical proximity of the uterus and cervix, the inhibitory effect of progesterone on uterine epithelial proliferation mediated through induction of stromal Hand2 that secondarily inhibits epithelial production of phospho-ERK is totally different than what are seen in the cervix following progesterone treatment, where neither Hand2 nor phospho-ERK, and the MAP kinase signaling pathway, appear to be progesterone targets. (poster)