Genetic Amplification of the NOTCH Modulator LNX2 Upregulates the WNT/β-Catenin Pathway in Colorectal Cancer

Abstract

Chromosomal copy number alterations (aneuploidy) define the genomic landscape of most cancer cells, but identification of the oncogenic drivers behind these imbalances remains an unfinished task. In this study, we conducted a systematic analysis of colorectal carcinomas that integrated genomic copy number changes and gene expression profiles. This analysis revealed 44 highly overexpressed genes mapping to localized amplicons on chromosome 13, gains of which occur often in colorectal cancers. RNAi-mediated silencing identified eight candidates whose loss of function reduced cell viability 20% or more in colorectal cancer cell lines. The functional space of the genes NUPL1, LNX2, POLR1D, POMP, SLC7A1, DIS3, KLF5, and GPR180 was established by global expression profiling after RNAi exposure. One candidate, LNX2, not previously known as an oncogene, was involved in regulating NOTCH signaling. Silencing LNX2 reduced NOTCH levels but also downregulated the transcription factor TCF7L2 and markedly reduced WNT signaling. LNX2 overexpression and chromosome 13 amplification therefore constitutively activates the WNT pathway, offering evidence of an aberrant NOTCH-WNT axis in colorectal cancer.

Gene‐dosage dependent overexpression at the 13q amplicon identifies DIS3 as candidate oncogene in colorectal cancer progression

“…Of these genes LNX2 was shown to activate the WNT pathway (Camps et al, 2013). For this particular gene we were able to confirm the gene dosage-dependent overexpression in CRC but could not find overexpression in carcinomas compared with adenomas (data not shown).…”

“…Interestingly, CDK8, located at 13q12, has also been reported to function as an oncogene in CRC by driving b-catenin activity (Firestein et al, 2008). These and other findings indicate that several genes at the 13q amplicon are involved in pathways important for CRC carcinogenesis (Firestein et al, 2008;Salari et al, 2012;Shi et al, 2012;Camps et al, 2013;Day et al, 2013). The fact that the frequently observed high-level gain of chromosome 13 in CRC encompasses a large genomic region also suggests that multiple genes located there may be of functional relevance in the progression from adenoma to carcinoma.…”

“…Activation of LNX2 by amplification of its locus at 13q12.2 has recently been demonstrated to influence the WNT/b-catenin pathway in CRC (Camps et al, 2013). Interestingly, CDK8, located at 13q12, has also been reported to function as an oncogene in CRC by driving b-catenin activity (Firestein et al, 2008).…”

AMACRAmplification in Myxofibrosarcomas: A Mechanism of Overexpression That Promotes Cell Proliferation with Therapeutic Relevance

“…There are several long complex amplicons on 5p with multiple discontinuous cores encompassing potential driver genes (6,8). Integration or cross-referencing between genomic and transcriptomic profiling datasets may simplify determination of genuine driver oncogenes, whose consistent overexpression can confer growth advantages on cancer cells in which they are amplified (8,(22)(23)(24). Among the candidate drivers on 5p, AMACR was differentially upregulated in myxofibrosarcoma tissues, in both the published transcriptome and LCM-isolated sarcoma cells quantified for mRNA abundance (6,8).…”

Decreased Anxiety-Related Behaviour but Apparently Unperturbed NUMB Function in Ligand of NUMB Protein-X (LNX) 1/2 Double Knockout Mice

“…NUMB is a negative regulator of Notch signalling, and degradation of NUMB upon LNX1 overexpression was shown to moderately enhance Notch signalling in cultured cells [ 4 ]. However, LNX2 knockdown in colorectal cancer cell lines caused a decrease in NUMB levels, a result that does not fit with the notion of LNX2 targeting NUMB for degradation [ 6 ]. Developmentally, expression of both Lnx1 and Lnx2 messenger RNA (mRNA) is prominent in the embryonic and adult central nervous system (CNS) [ 1,2 ].…”