MRP
The MRP/ABCC family contains nine members (MRPs1-9, ABCCs 1-6 and ABCCs 10-12, respectively) with sizes from 1325 to 1545 amino acids. This probably completes the family, as there are no other putative MRP/ABCC genes among the 49 human ABC transporter genes. ABCC7/CFTR is a chloride channel, and as such is not considered a transporter. ABCC8/SUR1 and ABCC9/SUR2, the sulfonylurea receptors, are the ATPsensing subunits of a complex potassium channel and are not known to transport any substrates. ABCC8/SUR1 and ABCC9/SUR2 are intracellular ATP/ADP sensors, regulating the permeability of specific K-channels. Mutations in CFTR/ABCC7 cause cystic fibrosis, and mutations in the ABCC8/ SUR1 underlie a genetic disorder known as persistent hyperinsulinemic hypoglycemia of infancy. MRP10/ABCC13 is clearly a pseudo-gene which encodes a truncated protein highly expressed in fetal human live with the highest similarity to MRP2/ABCC2 but without transporting activity. MRP10/ABCC13 is considered the result of degenerative process due to deletion of exons encoding the NH2- terminal region of a progenitor relatively closely related to MRP1/ABCC1.
These four ABCC members do not transport any substrates. The MRP/ABCCs, CFTR/ABCC7, and the SUR1 & 2 are considered to evolve from a common ancestor, and these proteins are now grouped together in the C branch of the ABC transporter family. The most striking thus far is the absence of Mrp8/ABCC11 in mice. It is important to precisely define the substrate specificities of all human MRP/ABCC members as this will provide critical information on their physiological, pharmacological, and toxicological roles. Identification of xenobiotic substrates may suggest a potential role of the MRP/ABCC transporting proteins in clinical drug resistance and in protection against a wide range of environmental toxicants. Identification of exogenous substrates of the MRP/ABCC proteins has heavily relied on an assessment of their ability to confer resistance to candidate cytotoxic drugs and xenobiotics.
These four ABCC members do not transport any substrates. The MRP/ABCCs, CFTR/ABCC7, and the SUR1 & 2 are considered to evolve from a common ancestor, and these proteins are now grouped together in the C branch of the ABC transporter family. The most striking thus far is the absence of Mrp8/ABCC11 in mice. It is important to precisely define the substrate specificities of all human MRP/ABCC members as this will provide critical information on their physiological, pharmacological, and toxicological roles. Identification of xenobiotic substrates may suggest a potential role of the MRP/ABCC transporting proteins in clinical drug resistance and in protection against a wide range of environmental toxicants. Identification of exogenous substrates of the MRP/ABCC proteins has heavily relied on an assessment of their ability to confer resistance to candidate cytotoxic drugs and xenobiotics.