B-Myb Expression in Vascular Smooth Muscle Cells Occurs in a Cell Cycle-dependent Fashion and Down-regulates Promoter Activity of Type I Collagen Genes

doi:10.1074/jbc.271.7.3359

B-Myb Expression in Vascular Smooth Muscle Cells Occurs in a Cell Cycle-dependent Fashion and Down-regulates Promoter Activity of Type I Collagen Genes (*)

From the Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118

^§To whom correspondence should be addressed:
Dept. of Biochemistry, Boston University School of Medicine, 80 East Concord St., Boston MA 02118.
Tel.: 617-638-4120; Fax: 617-638-5339.

Abstract

The members of the Myb family of transcription factors are defined by homology in the DNA-binding domain; all bind the Myb-binding site (MBS) sequence (YG(A/G)C(A/C/G)GTT(G/A)). Here we report that cultured bovine vascular smooth muscle cells (SMCs) express B-myb. Levels of B-myb RNA found in exponential growth were reduced dramatically in serum-deprived quiescent SMCs; B-myb mRNA levels increased in the cell cycle during the late G to S phase transition following restimulation with serum, epidermal growth factor, or phorbol ester plus insulin-like growth factor-1. Changes in the rate of B-myb gene transcription could account for part of the observed increase following serum addition. Treatment of SMC cultures with actinomycin D indicated a >4-h half-life for B-myb mRNA during the S phase of the cell cycle. Cotransfection of either a bovine or human B-myb expression vector down-regulated the activity of a multimerized MBS element-driven reporter construct in SMCs. Putative MBS elements were detected upstream of the promoters of the two chains of type I collagen, which we have found to be expressed inversely with growth state of the SMC (Kindy, M. S., Chang, C.-J., and Sonenshein, G. E.(1988) J. Biol. Chem. 263, 11426-11430). In cotransfection experiments, B-myb expression down-regulated the promoter activity of α1(I) and α2(I) collagen constructs an average of 92 and 82%, respectively. Thus, B-myb represents a potential link in the observed inverse relationship between collagen gene expression and growth of vascular SMCs.

Footnotes

↵* This work was supported by National Institutes of Health Grant HL13262 (to G. E. S.) and Training Grant HL07429 (to D. J. M.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵¹ The abbreviations used are:

SMCs

smooth muscle cells

MBS

Myb-binding site

DMEM

Dulbecco's modified Eagle's medium

FBS

fetal bovine serum

EGF

epidermal growth factor

TPA

12-O-tetradecanoylphorbol-13-acetate

IGF-1

insulin-like growth factor-1

kb

kilobase(s)

bp

base pair(s)

CAT

chloramphenicol acetyltransferase

TK

thymidine kinase.
↵²D. Marhamati, R. Bellas, M. Arsura, and G. E. Sonenshein, manuscript in preparation.
- Received August 14, 1995.
- Revision received November 3, 1995.