Multidrug resistance-associated protein 9 (ABCC12) is present in mouse and boar sperm

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• The multidrug resistance-associated protein 9 (MRP9; ABCC12) gene produces various alternatively spliced RNAs in humans and mice.
• Previous research suggested the existence of a truncated 100 kDa MRP9 protein, but its presence remains unconfirmed.

Purpose of the Study:

• To characterize the full-length human and murine MRP9 protein, including its expression, localization, and functional properties.
• To investigate the post-translational modifications and substrate transport capabilities of MRP9, comparing it to other MRP family members.

Main Methods:

• Utilized a panel of monoclonal antibodies for detecting MRP9 protein expression in various tissues and cell lines.
• Employed immunolocalization microscopy and cell fractionation techniques to determine MRP9 subcellular localization.
• Investigated N-linked glycosylation status and tested for transport of known MRP substrates using transfected HEK-293 cells.

Main Results:

• Full-length Mrp9 was exclusively detected in testicular germ cells and mouse sperm, with no evidence of the previously reported truncated form.
• Murine Mrp9 and human MRP9 expressed in HEK-293 cells did not appear to be N-linked glycosylated.
• MRP9 localizes to the sperm midpiece but not to mitochondria; in HEK-293 cells, it is primarily found in the endoplasmic reticulum.
• MRP9 did not transport substrates typically transported by other MRP proteins, such as drug conjugates and organic anions.

Conclusions:

• The full-length MRP9 protein is specifically expressed in male germ cells and sperm, distinct from other characterized MRPs.
• MRP9's localization to the endoplasmic reticulum and lack of typical MRP substrate transport suggest a unique function.
• The absence of N-linked carbohydrates and mitochondrial localization further differentiate MRP9 from other members of the MRP family.