Receptor for the globular heads of C1q (gC1q‐R, p33, hyaluronan‐binding protein) is preferentially expressed by adenocarcinoma cells

Abstract

Combinatorial Ig libraries with phage display allow in vitro generation of human Ig fragments without the need to maintain hybridomas in ongoing cell culture or to select circulating Ig from human serum. Identifying tumor-associated antigens on the surface of intact tumor cells, as opposed to purified proteins, presents a challenge due to the difficulty of preserving complex 3-D epitopic sites on the cell surface, the variable expression of antigens on different malignant cell types and the stereotactic interference of closely associated proteins on the intact membrane surface limiting accessibility to antigenic sites. A combinatorial Ig library of 10 10 clones was generated from the cDNA of PBMCs derived from patients with breast adenocarcinoma. Following subtractive panning, the library was enriched for Ig (Fab fragment) binding to intact adenocarcinoma cells and the resultant Fabs were screened against a cDNA expression library, itself generated from breast cancer cells. Using this approach, we isolated clones from the cDNA library expressing gC1q-R, a glycoprotein comprising the major structure of C1, the first component of the complement system. gC1q-R is a 33 kDa glycoprotein expressed not only on the cell surface but also intracellularly, with motifs that target it to mitochondria and complete homology with HABP and human HeLa cell protein p32, which is copurified with pre-mRNA SF2. Sequencing of the gene encoding tumor-associated gC1q-R did not reveal any consistent tumor-specific mutations. However, histochemical staining with anti-gC1q-R MAb demonstrated marked differential expression of gC1q-R in thyroid, colon, pancreatic, gastric, esophageal and lung adenocarcinomas compared to their nonmalignant histologic counterparts. In contrast, differential expression was not seen in endometrial, renal and prostate carcinomas. Despite high expression in breast carcinoma, gC1q-R was also expressed in nonmalignant breast tissue. Although the precise relation of gC1q-R to carcinogenesis remains unclear, our finding of tumor overexpression and the known multivalent binding of gC1q-R to not only C1q itself but also a variety of circulating plasma proteins as well as its involvement in cell-to-cell interactions suggest that gC1q-R may have a role in tumor metastases and potentially serve in molecule-specific targeting of malignant cells.

The contribution of gC1qR/p33 in infection and inflammation

“…Although a direct functional link between these two proteins remains to be investigated more thoroughly, this observation suggests that the transient association of gC1qR with the cytoplasmic tail of MT1-MMP is likely to be involved in the mechanisms regulating presentation of the protease at the tumor cell surface where gC1qR expression has been shown to be enhanced in a tumor cell-specific manner (Rubinstein et al, 2004).…”

“…This hypothesis was put to the test by experiments in which a combinatorial immunoglobulin (Ig) library of 10 10 clones was first generated from the cDNA of primary breast adenocarcinoma cells (Rubinstein et al, 2004). Following subtractive panning, the library was enriched for Ig (Fab fragment) binding to intact adenocarcinoma cells and the resultant Fab was screened against a cDNA expression library generated from breast cancer cells.…”

“…Using this approach, clones were isolated from the cDNA library expressing gC1qR. Sequencing of the gene encoding tumor-associated gC1qR did not reveal any consistent tumor-specific mutations (Rubinstein et al, 2004). However, histochemical staining with anti-gC1qR monoclonal antibody demonstrated marked differential expression of gC1qR in thyroid, colon, pancreatic, gastric, esophageal, and lung adenocarcinomas as compared to non-malignant histologic counterparts (Rubinstein et al, 2004).…”

Chaperone-like protein p32 regulates ULK1 stability and autophagy

“…[2][3][4][5] Many human tumors exhibit higher p32 expression levels than their nonmalignant counterpart tissues. [6][7][8][9] Depleting p32 in human cancer cells strongly shifts their metabolism from oxidative phosphorylation to glycolysis. 1 Consistently, p32 knockout causes mid-gestation lethality of knockout embryos and defects in oxidative phosphorylation.…”

“…Mouse embryonic fibroblasts (MEFs) generated from p32 knockout embryos exhibited impaired ATP production and reduced mitochondrial membrane potential, which is in agreement with the observation that p32 silencing leads to increased mitochondrial fragmentation. 10,11 Notably, p32 was found to form protein complex with a variety of molecules 7,12,13 and has been suggested that it may act as a multifunctional chaperone protein. [12][13][14] ULK1 has a crucial role in mitophagy induction.…”