Breast Carcinoma Epithelial Cells Express a Very Low‐Density Lipoprotein Receptor Variant Lacking the O‐Linked Glycosylation Domain Encoded by Exon 16, But with Full Binding Activity for Serine Proteinase/Serpin Complexes and M_r‐40000 Receptor‐Associated Protein

Abstract

Very-low density lipoprotein receptor (VLDLR) belongs to the low-density lipoprotein receptor family of endocytosis receptors. It binds a variety of different ligands, including apolipoprotein E, Mr-40 000 receptor-associated-protein (RAP), and some serine proteinase/serpin complexes. We previously demonstrated the occurrence of two forms of VLDLR in SDS/PAGE, migrating with M,. 105000 and M , 130000, respectively [Heegaard, C. W., Simonsen, A. C. W., Oka, K., Kjflller, L., Christensen, A., Madsen, B., 270,. We now demonstrate that these two forms correspond to forms with the absence (type-11) and presence (type-I) of the 0-linked glycosylation domain encoded by exon 16, respectively. We show that the two forms have the same binding affinity to RAP and serine proteinase/serpin complexes. Using reverse transcription and PCR, we demonstrate that the splice variation giving rise to the two forms is highly cell specific. In particular, we demonstrate that human breast carcinomas express predominantly or exclusively the variant lacking exon 16. By immunohistochemistry, we demonstrate that VLDLR is mainly expressed by the epithelial cancer cells in these carcinomas. The VLDLR variant expressed by epithelial cancer cells could function in the clearance of cell-surface-associated serine proteinase/serpin complexes in breast carcinomas.Keywords: very-low-density-lipoprotein receptor; breast carcinoma; urokinase-type plasminogen activator; plasminogen-activator inhibitor 1 ; 40-kDa receptor-associated protein.The low-density lipoprotein receptor (LDLR) family comprises a group of multifunctional endocytosis receptors. The presently known mammalian members of the family are the following: LDLR itself, a,-macroglobulin receptor/low-density lipoprotein receptor-related protein (a2MFULRP) ; glycoprotein 330/megalin (gp330/megalin); very low-density lipoprotein receptor (VLDLR) (see reviews by Andreasen et al., 1994;Gliemann et al., 1994;Strickland et al., 1994), and the recently cloned apolipoprotein E receptor-2 (apoER-2) (Kim Correspondence to P. M.

Genomic loss and epigenetic silencing of very-low-density lipoprotein receptor involved in gastric carcinogenesis

“…Several candidate TSGs, such as ANKRD15 in renal cell carcinoma (Sarkar et al, 2002) and SMARCA2 in lung cancer (Reisman et al, 2003), were identified as targets for this 9p24.2-24.3 region. Among other genes located within this region, VLDLR has been also reported to be involved in the pathogenesis of GC and other cancers (Martensen et al, 1997;Nakamura et al, 2000;Chen et al, 2005). However, the association between genomic loss or epigenetic silencing of the VLDLR gene and gastric carcinogenesis has not been reported before.…”

“…Expression of several possible cancer-related target genes in the homozygous deletion at 9p24.2-24.3 The homozygously deleted region identified in the HSC58 cell line at 9p24.2-24.3 contains some genes, Silencing of VLDLR in gastric cancer H Takada et al which have been reported as cancer-related genes, including VLDLR (Martensen et al, 1997;Nakamura et al, 2000), ANKRD15 (Sarkar et al, 2002) and SMARCA2 (Reisman et al, 2003). Therefore, we next determined expression levels of VLDLR, ANKRD15 and SMARCA2 with other genes within the homozygously deleted region by means of reverse transcription (RT)-PCR in all 32 GC cell lines and in normal stomach.…”

“…Differences in ligand specificity and tissue distribution suggest that the VLDLR isoforms play distinct roles in various tissues and cells. Previous reports have demonstrated that VLDLR isoforms were also expressed in a variety of cancer tissues (Martensen et al, 1997;Nakamura et al, 2000), including gastric cancer (GC) (Chen et al, 2005), suggesting that the presence of VLDLR is likely to be associated with the pathogenesis of various cancers. VLDLR may serve as an energy source for the rapid growth of cancer cells or may contribute to tumor formation through ligands such as urokinase-plasminogen activator (uPA) and uPA-plasminogen activator inhibitor-1 complex (Webb et al, 1999).…”

Identification of Alternative Splicing Markers for Breast Cancer

“…In addition, we confirmed the cancer-specific splicing pattern of the mRNA encoding the very low density lipoprotein receptor, VLDLR. The VLDLR alternative splicing pattern may be due to the epithelial origin of cancer cells (46).…”

Ligand Binding Properties of the Very Low Density Lipoprotein Receptor

“…One variation affects exon 16, encoding the O-linked sugar domain. VLDLR-II, lacking the O-linked sugar domain, binds the M r 40,000 receptor-associated protein (RAP) and serine proteinase-serpin complexes with the same affinity as VLDLR-I (25). A second variation affects exon 4, encoding the third (CTR-3) out of the total eight CTRs.…”