Myosin heavy chain isoform expression in human myometrium: Presence of an embryonic nonmuscle isoform in leiomyomas and in cultured cells

Abstract

We had previously found no myosin heavy chain (MHC) changes in expression during pregnancy in human myometrium. In the present work, we compared the MHC pattern of expression in normal human myometrium, pregnant and non-pregnant, to that in benign tumors of the uterine musculature and in cultured myometrial cells. We used a high-resolution gel electrophoretic system and monoclonal antibodies directed against smooth muscle and nonmuscle MHCs. Smooth muscle MHCs (SM1, 204 kDa, and SM2, 200 kDa, MHCs) and a nonmuscle MHC of 196 kDa (NM MHC) were detected in pregnant and nonpregnant human myometrium. Pregnant myometrium was found to differ from nonpregnant myometrium by its slightly lower content in NM MHC, whereas the ratio of SM1/SM2 was equivalent. In leiomyomas and in cultured cells grown from human myometrium explants, SM1, SM2, and NM MHCs were also expressed. In addition, a nonmuscle MHC of 198/200 kDa (SMemb MHC), which was present in a fetal human uterus but not in adult normal tissue, was observed in leiomyomas and in cultured cells. Expression of SM1 and SM2 MHCs was variable in the different leiomyomas studied. In cultured cells, SM1 and SM2 MHC content was low, but it was enhanced by suppression of serum after cell confluency. Present results confirm that pregnancy-associated smooth muscle cell hypertrophy is not accompanied by major changes in MHCs. In contrast, cell culturing and cell hyperplasia leading to leiomyoma formation induce substantial modifications in MHCs, including the occurrence of a second type of nonmuscle MHC.

Comparative Analysis of Smooth Muscle Isoactin Gene Expression in Normal and Neoplastic Tissues

“…This observation is consistent with prior studies which have shown that leiomyomas remain highly differ entiated and express several contractile proteins found in normal smooth muscle [40][41][42][43]. Interestingly, molecular studies identified at least two distinct subpopulations of uterine leiomyomas: (1) those which displayed high levels of smooth muscle isoactin gene expression and possessed a muscle:nonmuscle isoactin ratio similar to that ob served in normal uterine smooth muscle and (2) those which displayed low levels of smooth muscle isoactin gene expression and possessed a musclc:nonmuscle isoactin ratio similar to that observed in cellular leiomyomas.…”

Expression of RND Proteins in Human Myometrium1

“…Myometrial cells were isolated using a minced tissue explants method [32] and cultured as described by Phaneuf et al [33]. Pre-confluent cells were seeded onto cover slips and transfected with eukaryotic expression vectors pRK5 encoding myc-tagged RND2 or RND3 using Lipofectamine according to the supplier's instructions.…”

Expression of non-muscle myosin isoforms in rabbit myometrium is estrogen-dependent

“…Eddinger and Wolf (1993) have found that the expression of the NM1 (198 kDa) and NM2 (196 kDa) isoforms in mouse uterus follows the same pattern described here for rabbit myometrium. Similarly, Morano et al (1993) reported a diminution of 198-kDa NMMyHC during gestation in the rat, and Cavaillé et al (1995) have seen a decrease in the 196-kDa NM-MyHC variant in human pregnant myometrium.…”

“…Since estrogens are involved in cellular proliferation (Travers and Knowler 1987) and probably induce the division of myometrial SMC both in vivo (Kirkland et al 1979;Mukku et al 1981) and in vitro (Boulet and Fortier 1987), it is tempting to speculate that the expression of this isoform is related to cellular hyperplasia. Cavaillé et al (1995) have reported that in human myometrium the expression of the 198-/200-kDa B-type NM-MyHC isoform correlated with neoproliferative phenomena, but not with changes in the growth pattern observed during pregnancy.…”

“…Some authors have reported the presence of NM myosin isoforms in rat uterus during development (Eddinger and Wolf 1993) and pregnancy (Morano et al 1993), but with no precise correlation with estrogen level. In a more recent study, Cavaillé et al (1995) have shown that, in human, the developing myometrium contains a 200-kDa B-type MyHC (Kuro-o et al 1991) that is down-regulated with development and that is re-expressed in leiomyoma but not during pregnancy. In this study, we wish to establish whether: (1) NM myosin is also present in the SMC of rabbit myometrium, and (2) specific levels of estrogens can, like to thyroid hormones, affect the expression of NM myosin during pregnancy and ovariectomy.…”