PLASTICITY OF VASCULAR SMOOTH-MUSCLE ALPHA-ACTIN GENE-TRANSCRIPTION -CHARACTERIZATION OF MULTIPLE, SINGLE-STRAND, AND DOUBLE-STRAND SPECIFIC DNA-BINDING PROTEINS IN MYOBLASTS AND FIBROBLASTS

Transcriptional activity of the mouse vascular smooth muscle (VSM) alp ha-actin promoter was governed by both cell type and developmental sta ge-specific mechanisms, A purine-rich motif (PrM) located as -181 to - 176 in the promoter was absolutely required for activation in mouse AK R-2B embryonic fibroblasts and partially contributed to activation in undifferentiated mouse BC3H1 myoblasts, Transcriptional enhancer facto r 1 recognized the PrM and cooperated with other promoter binding prot eins to regulate serum growth factor -dependent transcription in both myoblasts and fibroblasts, Two distinct protein factors (VAC-ssBF1 and VAC-ssBF2) also were identified that bound sequence specifically to s ingle-stranded oligonucleotide probes that spanned both the PrM and a closely positioned negative regulatory element, VAC-ssBF1 and BF2 bind ing activity was detected in undifferentiated myoblasts, embryonic fib roblasts, and several smooth muscle tis sues in the mouse and human, A myoblast-specific pro tein (VAC-RF1) also was detected that bound dou ble-stranded probes containing a CArG-like sequence that previously wa s shown to impart strong, cell type specific repression, The binding a ctivity of transcription en hancer factor 1, VAC-RF1, and VAC-ssBF1 wa s significantly diminished when confluent BC3H1 myoblasts differentiat ed into myocytes and expressed VSN alpha-actin mRNA after exposure to serum-free medium, The results indicated that cell type-specific contr ol of the VSM alpha-actin gene promoter required the participation of multiple DNA binding proteins, including two that were enriched in smo oth muscle and had preferential affinity for single-stranded DNA.