STAT 5a and 5b are members of the STAT family of transcription factors, part of the JAK/STAT signal transduction pathway, and approximately 90% identical at the amino acid level. When inactive, STATs are cytoplasmic. Upon ligand binding and activation of a cytokine receptor, the receptor binds to a member of the JAK family. The receptor is phosphorylated and recruits a member of the STAT family that is then phosphorylated. It then dimerizes and is transported into the nucleus, where it can act as a transcription factor. In all, there are about 38 cytokines that signal through their cytokine receptors and through the JAK/STAT pathway to cause downstream transcriptional effects. Interestingly, these effects seem to be cell-type specific and JAK/STAT specific. To name a few, STAT5s respond to cellular stimulation by IL-2, IL-3, IL-5, IL-7, GM-CSF, IFN-g, insulin, erythropoietin, growth hormone, and prolactin.

STAT5a and 5b are involved in different types of cancer (including breast and prostate), inflammatory responses, and allergic reactions. STAT5s also prevent apoptosis in certain cell types and diseases based on their role as transcription factors and the genes they regulate. Due to the transcriptional control provided by the STAT family of proteins, their role in intracellular signaling, and their significance in diseases such as cancer and inflammation, this important signaling pathway is the subject of a number of basic research and pharmacological studies. This kit provides the assay-specific components for the quantitative determination of endogenous STAT 5a and STAT 5b  in human, mouse, and rat cell lysates.