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) alpha-actin promoter was governed by both cell type and developmental stage-specific mechanisms, A purine-rich motif (PrM) located as -181 to -176 in the promoter was absolutely required for activation in mouse AKR-2B embryonic fibroblasts and partially contributed to activation in undifferentiated mouse BC3H1 myoblasts, Transcriptional enhancer factor 1 recognized the PrM and cooperated with other promoter binding proteins 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 single-stranded oligonucleotide probes that spanned both the PrM and a closely positioned negative regulatory element, VAC-ssBF1 and BF2 binding activity was detected in undifferentiated myoblasts, embryonic fibroblasts, and several smooth muscle tis sues in the mouse and human, A myoblast-specific pro tein (VAC-RF1) also was detected that bound double-stranded probes containing a CArG-like sequence that previously was shown to impart strong, cell type specific repression, The binding activity of transcription en hancer factor 1, VAC-RF1, and VAC-ssBF1 was significantly diminished when confluent BC3H1 myoblasts differentiated into myocytes and expressed VSN alpha-actin mRNA after exposure to serum-free medium, The results indicated that cell type-specific control of the VSM alpha-actin gene promoter required the participation of multiple DNA binding proteins, including two that were enriched in smooth muscle and had preferential affinity for single-stranded DNA.