Spontaneous metastasis xenograft models link CD44 isoform 4 to angiogenesis, hypoxia, EMT and mitochondria‐related pathways in colorectal cancer

Abstract

Hematogenous metastasis limits the survival of colorectal cancer (CRC) patients. Here, we illuminated the roles of CD44 isoforms in this process. Isoforms 3 and 4 were predominantly expressed in CRC patients. CD44 isoform 4 indicated poor outcome and correlated with epithelial‐mesenchymal transition (EMT) and decreased oxidative phosphorylation in patients; opposite associations were found for isoform 3. Pan‐CD44 knockdown (kd) independently impaired primary tumor formation and abrogated distant metastasis in CRC xenografts. The xenograft tumors mainly expressed the clinically relevant CD44 isoforms 3 and 4. Both isoforms were enhanced in the paranecrotic, hypoxic tumor regions but were generally absent in lung metastases. Upon CD44 kd, tumor angiogenesis was increased in the paranecrotic areas, accompanied by reduced HIF‐1α and CEACAM5 but increased E‐cadherin expression. Mitochondrial genes and proteins were induced upon pan‐CD44 kd, as were oxidative phosphorylation genes. Hypoxia increased VEGF release from tumor spheres, particularly upon CD44 kd. Genes affected upon CD44 kd in xenografts specifically overlapped concordantly with genes correlating with CD44 isoform 4 (but not isoform 3) in patients, validating the clinical relevance of the used model and highlighting the metastasis‐promoting role of CD44 isoform 4.

RNA-binding proteins regulating the CD44 alternative splicing

“…All of the above-mentioned findings suggest that both CD44 isoform 3 and isoform 4 are expressed in cancer cells but play distinct roles in the different steps of cancer development. Thus, as it has been partially shown in colon cancer, CD44 isoform 4 can play an anti-tumor role during the initial malignant transformation but may later benefit metastasis formation (Everest-Dass et al, 2023). In gallbladder cancer CD44 isoform 4 is associated with a mesenchymal phenotype, increased chemotaxis, increased invasiveness, but lower tumorigenicity (Miwa et al, 2017).…”

“…frontiersin.org 2012), gastric (Ishimoto et al, 2011;Lau et al, 2014), bladder (Miyake et al, 2002), esophageal (Kagami et al, 2018), gallbladder cancer (Yamaguchi et al, 2000), thyroid (Kawai et al, 2019), ovarian (Sosulski et al, 2016), colorectal cancer (Boman et al, 2023;Everest-Dass et al, 2023), melanoma (Zhang et al, 2016) and leukemia as well (Holm et al, 2015). While in breast, esophageal, and gallbladder cancer CD44 isoform 3 is associated with a more metastatic phenotype and poor prognosis [e.g., (Yamaguchi et al, 2000;Yae et al, 2012;Kagami et al, 2018)], it does not do so in ovarian cancer (Sosulski et al, 2016).…”

“…While in breast, esophageal, and gallbladder cancer CD44 isoform 3 is associated with a more metastatic phenotype and poor prognosis [e.g., (Yamaguchi et al, 2000;Yae et al, 2012;Kagami et al, 2018)], it does not do so in ovarian cancer (Sosulski et al, 2016). Sometimes, e.g., in the case of colorectal cancer, CD44 isoform 3 has been shown associated with both poor prognosis/higher recurrence rate (Yamaguchi et al, 2016) and good prognosis/lower recurrence rate (Mashita et al, 2014;Everest-Dass et al, 2023), pointing to the possible greater significance of the ratio of CD44 isoforms. Indeed, the high ratio of CD44 isoform 4/CD44 variant exon v9 in patients with colorectal cancer shows a significantly poorer prognosis than the low CD44 isoform 4/CD44 variant exon v9 ratio (Mashita et al, 2014).…”