BMPR2

Bone morphogenetic protein receptor type II or BMPR2 is a serine/threonine receptor kinase. It binds Bone morphogenetic proteins, members of the TGF beta superfamily of ligands, which are involved in paracrine signalling. BMPs are involved in a host of cellular functions including osteogenesis, cell growth and cell differentiation. Signaling in the BMP pathway begins with the binding of a BMP to the type II receptor. This causes the recruitment of a BMP type I receptor, which it phosphorylates. The Type I receptor phosphorylates an R-SMAD a transcriptional regulator.

Function

Unlike the TGFβ type II receptor, which has a high affinity for TGF-β1, BMPR2 does not have a high affinity for BMP-2, BMP-7 and BMP-4, unless it is co-expressed with a type I BMP receptor. On ligand binding, forms a receptor complex consisting of two type II and two type I transmembrane serine/threonine kinases. Type II receptors phosphorylate and activate type I receptors which autophosphorylate, then bind and activate SMAD transcriptional regulators. Binds to BMP-7, BMP-2 and, less efficiently, BMP-4. Binding is weak but enhanced by the presence of type I receptors for BMPs.^[1] In TGF beta signaling all of the receptors exist in homodimers before ligand binding. In the case of BMP receptors only a small fraction of the receptors exist in homomeric forms before ligand binding. Once a ligand has bound to a receptor, the amount of homomeric receptor oligomers increase, suggesting that the equilibrium shifts towards the homodimeric form.^[1] The low affinity for ligands suggests that BMPR2 may differ from other type II TGF beta receptors in that the ligand may bind the type I receptor first.^[2]

Oocyte Development

BMPR2 is expressed on both human and animal granulosa cells, and is a crucial receptor for bone morphogenetic protein 15 (BMP15) and growth differentiation factor 9 (GDF 9). These two protein signaling molecules and their BMPR2 mediated effects play an important role in follicle development in preparation for ovulation.^[3] However, BMPR2 can’t bind BMP15 and GDF9 without the assistance of bone morphogenetic protein receptor 1B (BMPR1B) and transforming growth factor β receptor 1 (TGFβR1) respectively. There is evidence that the BMPR2 signaling pathway is disrupted in the case of polycystic ovary syndrome, possibly by hyperaldosterism.^[4]

It appears that the hormones estrogen and follicle stimulating hormone (FSH) have roles in regulating expression of BMPR2 in granulosa cells. Experimental treatment in animal models with estradiol with or without FSH increased BMPR2 mRNA expression while treatment with FSH alone decreased BMPR2 expression. However, in human granulosa-like tumor cell line (KGN), treatment with FSH increased BMPR2 expression.^[5]

Clinical significance

An inactivating mutation in the BMPR2 gene has been linked to primary pulmonary hypertension.^[6]

BMPR2 functions (among others) to inhibit the proliferation of vascular smooth muscle so when this gene is altered vascular smooth muscle proliferates and leads to pulmonary hypertension which among other things can lead to cor pulmonale. (robbins and cotran for usmle step 1).

References

External links

• BMPR2 gene variant database
• GeneReviews/NCBI/NIH/UW entry on Heritable Pulmonary Arterial Hypertension
• OMIM entries on Heritable Pulmonary Arterial Hypertension