Protocadherin LKC, a new candidate for a tumor suppressor of colon and liver cancers, its association with contact inhibition of cell proliferation

Abstract

Protocadherins are a major subfamily of the cadherin superfamily, but little is known about their functions and intracellular signal transduction. We cloned a novel human protocadherin gene, containing seven EC domains, and identified functional aspects of this gene. The gene was predominantly expressed in liver, kidney and colon tissues, and was thus designated Protocadherin LKC. The expression of Protocadherin LKC is markedly reduced in cancers arising from these tissues at both transcriptional and protein levels. To investigate the effects of Protocadherin LKC expression in colon cancer, we introduced the gene into colon cancer cell line HCT116, which does not express this gene. Significantly, Protocadherin LKC expression induced contact inhibition of cell proliferation although it did not affect growth rate. When grown to post-confluence in monolayer cells cultures, Protocadherin LKC-expressing HCT116 no longer formed multiple cell layers and showed the typical paving stone morphology of normal epithelial cells. Furthermore, expression of Protocadherin LKC suppressed tumor formation of HCT116 cells in a nude mouse model. In addition, we identified a protein, hMAST205 (microtubule-associated serine/threonine kinase-205 kDa), which interacted with Protocadherin LKC; the interaction occurring between the PDZ domain of hMAST205 and C-terminal tail of Protocadherin LKC. Our results suggest that Protocadherin LKC, which directly binds PDZ protein, is a molecular switch for contact inhibition of epithelial cells in the liver, kidney and colon tissues.

Protocadherin of the Liver, Kidney, and Colon Associates with Detergent-resistant Membranes during Cellular Differentiation

“…First, the limited access to anti-PLKC antibodies hampered these analyses, whereas the recombinant PLKC-YFP protein could be analyzed using commercially available anti-GFP antibodies that recognize the YFP variant of GFP. Second, wild type endogenous PLKC showed a similar cellular distribution as PLKC-YFP as assessed by anti-PLKC antibodies (1).…”

“…Characteristics of PLKC are seven extracellular cadherin repeats with 93-117 amino acids each and a 35-amino acidlong cytoplasmic domain that is terminated by a PDZ binding domain. An interaction with the PDZ domain of hMAST205 has been demonstrated, suggesting a possible role as a switch for intracellular signaling (1). The aim of this study was to investigate the structural features of PLKC, its biosynthesis, intracellular processing, and sorting during differentiation.…”

Functional epigenetics identifies a protocadherin PCDH10 as a candidate tumor suppressor for nasopharyngeal, esophageal and multiple other carcinomas with frequent methylation

“…Heterophilic interactions with other molecules may be more important for their physiologic functions, such as the involvement in signal transduction. For example, protocadherin LKC interacts with the PDZ domain-containing protein kinase hMAST205 (Okazaki et al, 2002). The Drosophila tumor suppressor protocadherin fat controls planar polarity through physical interactions with a transcriptional corepressor Atrophin (Fanto et al, 2003).…”

“…So far, three classical cadherins (CDH1, CDH13, CDH4) have been defined as functional TSGs with frequent epigenetic silencing in multiple tumors (Graff et al, 1995;Yoshiura et al, 1995;Toyooka et al, 2001;Miotto et al, 2004). Only one protocadherin, protocadherin LKC, was reported to inhibit tumor cell proliferation as a candidate TSG (Okazaki et al, 2002). Our study appears to be the first report that a protocadherin gene can function as a broad TSG, meanwhile being frequently inactivated epigeneti- PCDH10 as a broad tumor suppressor methylated in carcinomas J Ying et al cally in multiple carcinomas, including NPC, esophageal, hepatocellular, breast, cervical, lung and colorectal carcinomas.…”

“…Although its mouse homolog (mfat) behaves differently not like a TSG since it is frequently expressed in highly proliferative cells, its human FAT was recently found to be frequently hypermethylated in tumors although no functional study was performed (Paz et al, 2003). The protocadherin LKC is associated with contact inhibition of cell proliferation, and has been suggested as a candidate TSG for colon and liver cancer (Okazaki et al, 2002). Mutations in protocadherin 15 as well as CDH23 have also been implicated in Usher syndrome (Bolz et al, 2001;Di et al, 2001;Siemens et al, 2002), as recently demonstrated in a zebrafish model Sollner et al, 2004).…”