IRS4 (Insulin Receptor Substrate 4) is a signaling adapter protein that plays a critical role in the insulin signaling pathway. Here are the key functions and roles of IRS4 in human biology:

1. Insulin Signaling: IRS4 is part of the insulin signaling cascade, where it acts as an adaptor molecule linking the activated insulin receptor to downstream signaling pathways. This is crucial for the regulation of glucose homeostasis and metabolism.

2. Cell Growth and Proliferation: IRS4 participates in the modulation of cell growth and survival signals through pathways such as the PI3K/Akt pathway. These pathways are important for cellular responses to growth factors beyond insulin.

3. Tissue Specific Expression: IRS4 has tissue-specific roles, with expression primarily seen in certain tissues such as the hypothalamus and the placenta, suggesting its specialized functions in these regions.

4. Potential Role in Cancer: Studies have indicated that IRS4 may be involved in oncogenic processes, potentially contributing to the growth and survival of cancer cells in certain types of cancer, although this area requires further research.

For more information, you might want to check out the National Center for Biotechnology Information (NCBI) Gene database, which provides detailed genetic and functional information on IRS4.