Expression of smooth muscle caldesmon in developing chicken gizzard

A tale of two clones: Caldesmon staining in the differentiation of cutaneous spindle cell neoplasms

BACKGROUND

We sought to compare the sensitivity and specificity of 2 different caldesmon antibodies in differentiating leiomyosarcoma from other cutaneous spindle cell neoplasms.

METHODS

Representative cutaneous spindle cell neoplasms were identified, including leiomyosarcoma, atypical fibroxanthoma, dermatomyofibroma and spindle cell squamous cell carcinoma. Immunohistochemistry was performed with antibodies directed toward caldesmon, smooth-muscle actin (SMA) and desmin. Sensitivity and specificity were calculated using grades from 3 independent observers.

RESULTS

The sensitivity of caldesmon (Ventana) was 100% (95% CI 78.2%-100%) and the specificity was 8.3% (2.8%-18.4%). Because this stain appeared to be non-specific, additional testing was performed on the same set of specimens using a second caldesmon clone (H-caldesmon, Dako), which had a sensitivity of 53.9% (25.1%-80.8%) and specificity of 96.6% (88.1%-99.6%). The sensitivity and specificity of SMA were 85.7% (57.2%-98.2%) and 84.5% (72.6%-92.7%), respectively. The sensitivity of desmin was 53.3% (26.6%-78.7%) with a specificity of 100% (94.0%-100%).

CONCLUSIONS

The Ventana caldesmon clone is not specific to smooth muscle, a potential pitfall to laboratories using this clone. The staining pattern, sensitivity and specificity of the Dako H-caldesmon antibody clone are similar to results from prior studies. The sensitivity and specificity of the Dako clone support its use in smooth muscle identification as an additional marker in challenging cases.

In vitro growth of human urinary tract smooth muscle cells on laminin and collagen type I-coated membranes under static and dynamic conditions

This study investigates in vitro growth of human urinary tract smooth muscle cells under static conditions and mechanical stimulation. The cells were cultured on collagen type I- and laminin-coated silicon membranes. Using a Flexcell device for mechanical stimulation, a cyclic strain of 0-20% was applied in a strain-stress-time model (stretch, 104 min relaxation, 15 s), imitating physiological bladder filling and voiding. Cell proliferation and alpha-actin, calponin, and caldesmon phenotype marker expression were analyzed. Nonstretched cells showed significant better growth on laminin during the first 8 days, thereafter becoming comparable to cells grown on collagen type I. Cyclic strain significantly reduced cell growth on both surfaces; however, better growth was observed on laminin. Neither the type of surface nor mechanical stimulation influenced the expression pattern of phenotype markers; alpha-actin was predominantly expressed. Coating with the extracellular matrix protein laminin improved in vitro growth of human urinary tract smooth muscle cells.

Role of pp60(c-src) and p(44/42) MAPK in ANG II-induced contraction of rat tonic gastrointestinal smooth muscles

We examined the role of mitogen-activated protein kinase (p(44/42) MAPK) in ANG II-induced contraction of lower esophageal sphincter (LES) and internal anal sphincter (IAS) smooth muscles. Studies were performed in the isolated smooth muscles and cells (SMC). ANG II-induced changes in the levels of phosphorylation of different signal transduction and effector proteins were determined before and after selective inhibitors. ANG II-induced contraction of the rat LES and IAS SMC was inhibited by genistein, PD-98059 [a specific inhibitor of MAPK kinases (MEK 1/2)], herbimycin A (a pp60(c-src) inhibitor), and antibodies to pp60(c-src) and p(120) ras GTPase-activating protein (p(120) rasGAP). ANG II-induced contraction of the tonic smooth muscles was accompanied by an increase in tyrosine phosphorylation of p(120) rasGAP. These were attenuated by genistein but not by PD-98059. ANG II-induced increase in phosphorylations of p(44/42) MAPKs and caldesmon was attenuated by both genistein and PD-98059. We conclude that pp60(c-src) and p(44/42) MAPKs play an important role in ANG II-induced contraction of LES and IAS smooth muscles.

Determinants of the contractile properties in the embryonic chicken gizzard and aorta

Smooth muscle is generally grouped into two classes of differing contractile properties. Tonic smooth muscles show slow rates of force activation and relaxation and slow speeds of shortening (V(max)) but force maintenance, whereas phasic smooth muscles show poor force maintenance but have fast V(max) and rapid rates of force activation and relaxation. We characterized the development of gizzard and aortic smooth muscle in embryonic chicks to identify the cellular determinants that define phasic (gizzard) and tonic (aortic) contractile properties. Early during development, tonic contractile properties are the default for both tissues. The gizzard develops phasic contractile properties between embryonic days (ED) 12 and 20, characterized primarily by rapid rates of force activation and relaxation compared with the aorta. The rapid rate of force activation correlates with expression of the acidic isoform of the 17-kDa essential myosin light chain (MLC(17a)). Previous data from in vitro motility assays (Rover AS, Frezon Y, and Trybus KM. J Muscle Res Cell Motil 18: 103-110, 1997) have postulated that myosin heavy chain (MHC) isoform expression is a determinant for V(max) in intact tissues. In the current study, differences in V(max) did not correlate with previously published differences in MHC or MLC(17a) isoforms. Rather, V(max) was increased with thiophosphorylation of the 20-kDa regulatory myosin light chain (MLC(20)) in the gizzard, suggesting that a significant internal load exists. Furthermore, V(max) in the gizzard increased during postnatal development without changes in MHC or MLC(17) isoforms. Although the rate of MLC(20) phosphorylation was similar at ED 20, the rate of MLC(20) dephosphorylation was significantly higher in the gizzard versus the aorta, correlating with expression of the M130 isoform of the myosin binding subunit in the myosin light chain phosphatase (MLCP) holoenzyme. These results indicate that unique MLCP and MLC(17) isoform expression marks the phasic contractile phenotype.