GATA3 functions as a major regulator of T helper 2 (TH2) cell differentiation in immune cells. GATA3 expression is upregulated through IL-4 receptor signaling or the Notch-mediated pathway, which results in production of IL-4, IL-5, and IL-13 cytokines, responsible for preferential differentiation of TH2-cells. GATA3 has been shown to regulate early developmental processes of T cells, such as T cell commitment, positive selection, and post-commitment CD4+ T cell survival. In the mammary gland, GATA3 plays an important role in differentiation and commitment of luminal epithelial cells. In a mouse model, exogenous expression of GATA3 in undifferentiated breast carcinoma cells induces differentiation and suppresses spreading of the tumor cells, suggesting that GATA3 is involved in preventing malignancy of breast cancer. GATA3 has been reported to be essential in development of a variety of normal tissues. Defect in GATA3 results in hypoparathyroidism, sensorineural deafness and renal dysplasia (HDR syndrome).