Striking differences of LDL receptor-related protein 1B expression in mouse and human.

The low density lipoprotein (LDL) receptor-related protein 1B (LRP1B) is a member of the expanding LDL receptor family, and is closely related to LRP. It was discovered as a putative tumor suppressor, and is frequently inactivated in human malignant tissues. However, the expression pattern of LRP1B in normal human tissues was unclear. In the present study, we analyzed LRP1B expression in normal mouse and human tissues. By using RT-PCR, we found that, while mouse LRP1B expression is mostly restricted to the brain, human LRP1B expression is more widespread with highest expression levels detected in the brain, adrenal gland, salivary gland, and testis. Although mouse LRP1B expresses in the forms of both full-length receptor tail and an alternatively spliced form lacking a 33-amino acid insert, human LRP1B is expressed exclusively in the form of full-length receptor tail. Finally, we found that, unlike mouse LRP1B, human LRP1B is cleaved by furin. Taken together, these data demonstrate that there are striking differences between LRP1B expression in mouse and human tissues. The broader expression pattern of LRP1B in human tissues suggests that this putative tumor suppressor may play roles in several types of human cancer.