Expression of a recombinant full-length LRP1B receptor in human non-small cell lung cancer cells confirms the postulated growth-suppressing function of this large LDL receptor family member
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Arno G. Beer1,*, Christoph Zenzmaier1,2,*, Michael Schreinlechner1, Jenny Haas1, Martin F. Dietrich3, Joachim Herz3, Peter Marschang1
1Department of Internal Medicine, Medical University of Innsbruck, Innsbruck, Austria
2University of Applied Sciences Tyrol, Innsbruck, Austria
3Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX, USA
*These authors have contributed equally to this work
Peter Marschang, email: Peter.Marschang@i-med.ac.at
Keywords: low-density lipoprotein receptor-related protein 1B, tumor suppressor, proliferation, overexpression, siRNA
Received: February 15, 2016 Accepted: August 13, 2016 Published: September 8, 2016
Low-density lipoprotein (LDL) receptor-related protein 1B (LRP1B), a member of the LDL receptor family, is frequently inactivated in multiple malignancies including lung cancer. LRP1B is therefore considered as a putative tumor suppressor. Due to its large size (4599 amino acids), until now only minireceptors or receptor fragments have been successfully cloned. To assess the effect of LRP1B on the proliferation of non-small cell lung cancer cells, we constructed and expressed a transfection vector containing the 13.800 bp full-length murine Lrp1b cDNA using a PCR-based cloning strategy. Expression of LRP1B was analyzed by quantitative RT-PCR (qRT-PCR) using primers specific for human LRP1B or mouse Lrp1b. Effective expression of the full length receptor was demonstrated by the appearance of a single 600 kDa band on Western Blots of HEK 293 cells. Overexpression of Lrp1b in non-small cell lung cancer cells with low or absent endogenous LRP1B expression significantly reduced cellular proliferation compared to empty vector-transfected control cells. Conversely, in Calu-1 cells, which express higher endogenous levels of the receptor, siRNA-mediated LRP1B knockdown significantly enhanced cellular proliferation. Taken together, these findings demonstrate that, consistent with the postulated tumor suppressor function, overexpression of full-length Lrp1b leads to impaired cellular proliferation, while LRP1B knockdown has the opposite effect. The recombinant Lrp1b construct represents a valuable tool to unravel the largely unknown physiological role of LRP1B and its potential functions in cancer pathogenesis.
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