Protein kinase C phosphorylates both the light chains and the head portion of the heavy chains of brain myosin

Estrogen modulation of MgATPase activity of nonmuscle myosin-II-B filaments

The study tested the hypothesis that estrogen controls epithelial paracellular resistance through modulation of myosin. The objective was to understand how estrogen modulates nonmuscle myosin-II-B (NMM-II-B), the main component of the cortical actomyosin in human epithelial cervical cells. Experiments used human cervical epithelial cells CaSki as a model, and end points were NMM-II-B phosphorylation, filamentation, and MgATPase activity. The results were as follows: 1) treatment with estrogen increased phosphorylation and MgATPase activity and decreased NMM-II-B filamentation; 2) estrogen effects could be blocked by antisense nucleotides for the estrogen receptor-alpha and by ICI-182,780, tamoxifen, and the casein kinase-II (CK2) inhibitor, 5,6-dichloro-1-beta-(D)-ribofuranosylbenzimidazole and attenuated by AG1478 and PD98059 (inhibitors of epithelial growth factor receptor and ERK/MAPK) but not staurosporine [blocker of protein kinase C (PKC)]; 3) treatments with the PKC activator sn-1,2-dioctanoyl diglyceride induced biphasic effect on NMM-II-B MgATPase activity: an increase at 1 nm to 1 microM and a decrease in activity at more than 1 microM; 4) sn-1,2-dioctanoyl diglyceride also decreased NMM-II-B filamentation in a monophasic and saturable dose dependence (EC(50) 1-10 microM); 5) when coincubated directly with purified NMM-II-B filaments, both CK2 and PKC decreased filamentation and increased MgATPase activity; 6) assays done on disassembled NMM-II-B filaments showed MgATPase activity in filaments obtained from estrogen-treated cells but not estrogen-depleted cells; and 7) incubations in vitro with CK2, but not PKC, facilitated MgATPase activity, even in disassembled NMM-II-B filaments. The results suggest that estrogen, in an effect mediated by estrogen receptor-alpha and CK2 and involving the epithelial growth factor receptor and ERK/MAPK cascades, increases NMM-II-B MgATPase activity independent of NMM-II-B filamentation status.

Phosphorylation of vertebrate nonmuscle and smooth muscle myosin heavy chains and light chains

In this article we review the various amino acids present in vertebrate nonmuscle and smooth muscle myosin that can undergo phosphorylation. The sites for phosphorylation in the 20 kD myosin light chain include serine-19 and threonine-18 which are substrates for myosin light chain kinase and serine-1 and/or -2 and threonine-9 which are substrates for protein kinase C. The sites in vertebrate smooth muscle and nonmuscle myosin heavy chains that can be phosphorylated by protein kinase C and casein kinase II are also summarized. Original data indicating that treatment of human T-lymphocytes (Jurkat cell line) with phorbol 12-myristate 13-acetate results in phosphorylation of both the 20 kD myosin light chain as well as the 200 kD myosin heavy chain is presented. We identified the amino acids phosphorylated in the human T-lymphocytes myosin light chains as serine-1 or serine-2 and in the myosin heavy chains as serine-1917 by 1-dimensional isoelectric focusing of tryptic phosphopeptides. Untreated T-lymphocytes contain phosphate in the serine-19 residue of the myosin light chain, and in a residue tentatively identified as serine-1944 in the myosin heavy chain.

Expression of four myosin heavy chain isoforms with development in mouse uterus

In smooth muscle tissue, two or three isoforms of myosin heavy chain (MHC) have been reported (SM1, SM2, and/or NM). In mouse uterus tissue, four bands in the region of the MHC's can be resolved on high resolution SDS polyacrylamide gels. Western blots using smooth muscle (SM) MHC-specific and nonmuscle (NM) MHC-specific polyclonal antibodies show the upper two bands in the MHC region are SM isoforms, whereas the lower two bands are NM isoforms. One-dimensional peptide maps of these four bands show each to have a unique pattern of polypeptide fragments following alpha-chymotrypsin digestion. Developmental expression of myosin heavy chains (MHC) in mouse uterus, aorta, bladder, and stomach (6 ages, 10-150 days) was determined using tissue homogenates. In the uterus, both SM MHC's show an increase in relative content with increasing age, whereas the NM MHC's show a decrease. The mouse aorta shows a significant increase in the SM MHC's and a significant decrease in the NM MHC from day 10 to day 30, which is similar to data reported for the rat aorta. Whereas both the bladder and stomach contain relatively small amounts of NM MHC's (approximately 10% or less), these quantities do show decreases with development. The SM1:SM2 ratio for the uterus remains high (3.4 at 150 days) through development; the aorta, bladder, and stomach also start out high, but tend toward 1.0 in the 150-day animals. The presence of four MHC isoforms in the uterus with unique developmental regulation of expression is consistent with hypotheses of unique functional roles for these isoforms.

Immunohistochemical studies on the distribution of cellular myosin II isoforms in brain and aorta

The distribution of nonmuscle myosin isoforms in brain and aorta was studied by using polyclonal antibodies against two synthetic peptides selected from a region near the carboxyl terminus of bovine brain (peptide IIB) and human macrophage (peptide IIA) myosin. Immunoblots of brain homogenates and purified myosin showed two major bands stained by anti-peptide IIB (MIIB1 and MIIB2) and a minor band stained by anti-peptide IIA (MIIA2). Polyclonal anti-human platelet myosin antibodies did not react with MIIB isoforms. In cryosections from bovine, rat, and mouse brains, anti-peptide IIB stained most neuronal cells. In bovine cryosections, glial staining was also observed. In contrast, anti-peptide IIA and anti-platelet myosin antibodies primarily stained blood vessels. In bovine aorta, the anti-peptide antibodies recognized four bands, MIIB3, MIIB4, MIIA1, and MIIA2. Only MIIA2 was recognized by anti-human platelet myosin antibodies. In bovine aorta cryosections, anti-peptide IIB stained smooth muscle cells in tunica intima and tunica media but did not stain endothelial cells. Anti-peptide IIA stained smooth muscle cells in the tunica media, and endothelial cells of vaso vasorum but not of aorta. Only polyclonal anti-platelet myosin antibodies stained the endothelial cells of aorta tunica intima. These results indicate that multiple isoforms of cellular myosins exist in mammals, that these isoforms are expressed in a cell specific manner, and that the major myosin isoforms isolated from whole brain originate from neurons and, at least in bovine brain, from glia, but not from blood vessels.

Cytokinesis is more rapid in Ha-T24-ras transfected rat embryo fibroblasts than in non-transfected control cells

It has long been known that neoplastic cells are characterized by increases in cell motility. Earlier studies from this laboratory indicated that mitotic events were also altered in many tumor and experimentally transformed cells and that this included increases in metaphase duration and a reduction in the duration of cytokinesis. The studies presented in this paper were done to determine whether or not transfection of normal rat embryo fibroblasts by the Ha-T24-ras oncogene could also produce such alterations in mitotic events. The results obtained with the use of time lapse video microscopy indicate that neither the duration of metaphase nor the rate of chromosome movement during anaphase was altered but that the rate of furrow progression during cytokinesis occurred at a significantly more rapid rate. Thus, the cellular alterations induced by transfection with Ha-T24-ras accelerate microfilament-dependent cytokinetic furrowing without significant effects on microtubule-dependent mitotic events. One of several possible mechanisms that could account for these observations involves a down regulation of protein kinase C which has been reported to occur in many neoplastic cells including those transformed by ras. Such a hypothesis could also have broader implications because it may be applicable to the increase in motility and metastatic activity generally observed in transformed cells.