KRAS mutation‐independent downregulation of MAPK/PI3K signaling in colorectal cancer

Abstract

KRAS is a gatekeeper gene in human colorectal tumorigenesis. KRAS is 'undruggable'; hence, efforts have been diverted to inhibit downstream RAF/MEK/ERK and PI3K/Akt signaling. Nevertheless, none of these inhibitors has progressed to clinical use despite extensive trials. We examined levels of phospho-ERK1/2(T202/Y204) and phospho-Akt1/2/3(S473) in human colorectal tumor compared to matched mucosa with semiquantitative near-infrared western blot and confocal fluorescence immunohistochemistry imaging. Surprisingly, 75.5% (25/33) of tumors had lower or equivalent phospho-ERK1/2 and 96.9% (31/32) of tumors had lower phospho-Akt1/2/3 compared to matched mucosa, irrespective of KRAS mutation status. In contrast, we discovered KRAS-dependent SOX9 upregulation in 28 of the 31 (90.3%) tumors. These observations were substantiated by analysis of the public domain transcriptomics The Cancer Genome Atlas (TCGA) and NCBI Gene Expression Omnibus (GEO) datasets and proteomics Clinical Proteomic Tumor Analysis Consortium (CPTAC) dataset. These data suggest that RAF/MEK/ERK and PI3K/ Akt signaling are unlikely to be activated in most human colorectal cancer.

KRAS-specific antibody binds to KRAS protein inside colorectal adenocarcinoma cells and inhibits its localization to the plasma membrane

“…Phospho-ERK1/2 and phospho-Akt1/2/3 are known downstream effectors of KRAS in the MAPK signaling in cancer cell lines ( 21 ). However, we previously reported that phospho-ERK1/2 or phospho-Akt1/2/3 were not upregulated in CRC tumor compared to matched mucosa tissues, and in fact in most cases, downregulated in tumor ( 24 ). Instead, most CRC tumor tissues displayed upregulation of SOX9 compared to matched normal mucosa.…”

“…Furthermore, SOX9 were previously reported to be able to promote cancer cell proliferation and tumor progression by directly activating stem cell-like signaling and inhibit cell differentiation ( 43 ). Since we showed previously that the expression of SOX9 proteins in CRC was KRAS-mutant-dependent ( 24 ), treatment of CRC with anti-KRAS antibodies is expected to downregulate SOX9 protein expression. Thus, we counterstained the tumor cells for SOX9 after treatment with anti-KRAS antibodies.…”

“…In fact, to date, only one clinical trial (NCT02788279) has progressed past Phase 2 [reviewed by Xie, Chen ( 23 )]. Our recent study also reported the absence of MAPK and PI3K/Akt pathways activation in CRC tumors compared to matched normal mucosa indicating that phosphorylated ERK/AKT may not be the appropriate downstream effectors to repress KRAS signaling ( 24 ).…”

Circulating Nucleic Acids in Colorectal Cancer: Diagnostic and Prognostic Value

“…Disease Markers REST, pyQPCR, PrimerPy, GenEx, MultiD PowerNest, qBASE+ [122] KRAS mutation analysis Exists in 40% CRC cases mostly in codons 12 [36], negative predictive factor for metastatic CRC to treat with anti-EGFR antibodies [123], and correlates with the prognosis of the disease [124] Not declared COSMIC, TCGA, GSEA, GO enrichment, KEGG, STRING, CPTAC, [125][126][127] NGS assay:…”

Warning signs from the crypt: Aberrant protein glycosylation marks opportunities for early colorectal cancer detection.

“…β-catenin is aided by additional signaling pathways mediated by KRAS to drive gene transcription responsible for tumor growth and invasion ( 13 ). KRAS activates the downstream Raf-MEK-ERK pathway and PI3K/AKT signaling through mTOR ( 14 ). The loss of heterozygosity at chromosome 18q can lead to loss of function of tumor suppressor genes in this location including SMAD2/4 which are part of transforming growth factor-β (TGF-β) pathway ( 15 ).…”