Transforming growth factor-beta1 regulates cell growth and causes downregulation of SMemb/non-muscle myosin heavy chain B mRNA in human prostate stromal cells.

OBJECTIVES

SMemb/non-muscle myosin heavy chain B (SMemb/NMMHC-B) is most abundantly expressed in proliferating smooth muscle cells and correlates with phenotypic changes from a contractive to a proliferative type. The stromal cells of the prostate play a crucial role in the regulation of prostatic growth and function. The aim of this study was to investigate the effects of the multifunctional cytokine transforming growth factor-beta1 (TGF-beta1) on SMemb/NMMHC-B mRNA expression and stromal cell growth. The expression of the SM2 isoform of smooth muscle myosin heavy chain (SMMHC) mRNA was also examined.

MATERIAL AND METHODS

Primary cultures of prostate stromal cells were established by means of an explant method from eight normal prostates. The effects of TGF-beta1 on stromal cell growth were determined by means of a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide conversion assay. SMemb/NMMHC-B and SM2 mRNA expression were analyzed quantitatively by means of real-time polymerase chain reaction.

RESULTS

In the absence of TGF-beta1, cells expressed alpha-smooth muscle actin and vimentin. After TGF-beta1 treatment, the expression of alpha-smooth muscle actin increased and cells also expressed desmin. TGF-beta1 at concentrations of 1.0, 5.0 and 10 ng/ml suppressed cell growth by 72%, 62% and 56%, respectively, downregulated SMemb/NMMHC-B mRNA expression by 71%, 52% and 38%, respectively and upregulated SM2 mRNA expression 2.1-, 3.0- and 5.3-fold, respectively.

CONCLUSIONS

These results demonstrate that TGF-beta1 modulates the smooth muscle cell phenotype from a proliferative to a contractile type and that the inhibitory effects of TGF-beta1 on stromal cell growth correlate with downregulation of the SMemb/NMMHC-B gene.