SH2 domain-containing transforming protein C1 (SHC1), also known as SHCA, is a cytoplasmic adaptor protein that is important in the signal transduction from growth factor, cytokine, and lymphocyte antigen receptors. SHC1 contains a PTB/PID domain (aa 156-339), a collagen homology domain (aa 340-487), and an SH2 domain (aa 488-579). Alternate splicing generates additional isoforms that differ in the extent of N-terminal truncation. Activation of Shc1 by phosphorylation at Ser239, Ser240, and Tyr317 enables SHC1 to interact with the GRB2/SOS complex, leading to the transcription of genes involved in mitogenesis and apoptosis. The p46 and p52 isoforms promote mitogenic signaling, while the p66 isoform promotes apoptosis and functions as a negative regulator of SHC1-mediated mitogenic signal transduction.