The bone morphogenetic protein receptor, type IB is also known as BMPR1B or ALK6 is a protein which in humans is encoded by the BMPR1B gene. Bone morphogenetic proteins (BMPs) signal through the BMP type I and type II receptors to regulate cellular processes, including embryonic development. The type I BMP receptors activin-like kinase (ALK) 3 and ALK6 share a high degree of homology, yet possess distinct signaling roles. Decreased expression of BMPR-IB correlates with poor prognosis in breast cancer patients and leads to increased cell proliferation of breast cancer cells in vitro, and BMPR-IB mediates an inhibitory effect on breast cancer cells. Researchers found that BMP-2-induced apoptosis was mediated by BMP-RIB in osteoblasts and occurred independently of BMP-2-induced osteoblast differentiation.