Nuclear reprogramming and the cancer genome

Cytokeratin 19 (KRT19) has a Role in the Reprogramming of Cancer Stem Cell-Like Cells to Less Aggressive and More Drug-Sensitive Cells

Cytokeratin 19 (KRT19) is a cytoplasmic intermediate filament protein, which is responsible for structural rigidity and multipurpose scaffolds. In several cancers, KRT19 is overexpressed and may play a crucial role in tumorigenic transformation. In our previous study, we revealed the role of KRT19 as signaling component which mediated Wnt/NOTCH crosstalk through NUMB transcription in breast cancer. Here, we investigated the function of KRT19 in cancer reprogramming and drug resistance in breast cancer cells. We found that expression of KRT19 was attenuated in several patients-derived breast cancer tissues and patients with a low expression of KRT19 were significantly correlated with poor prognosis in breast cancer patients. Consistently, highly aggressive and drug-resistant breast cancer patient-derived cancer stem cell-like cells (konkuk university-cancer stem cell-like cell (KU-CSLCs)) displayed higher expression of cancer stem cell (CSC) markers, including ALDH1, CXCR4, and CD133, but a much lower expression of KRT19 than that is seen in highly aggressive triple negative breast cancer MDA-MB231 cells. Moreover, we revealed that the knockdown of KRT19 in MDA-MB231 cells led to an enhancement of cancer properties, such as cell proliferation, sphere formation, migration, and drug resistance, while the overexpression of KRT19 in KU-CSLCs resulted in the significant attenuation of cancer properties. KRT19 regulated cancer stem cell reprogramming by modulating the expression of cancer stem cell markers (ALDH1, CXCR4, and CD133), as well as the phosphorylation of Src and GSK3β (Tyr216). Therefore, our data may imply that the modulation of KRT19 expression could be involved in cancer stem cell reprogramming and drug sensitivity, which might have clinical implications for cancer or cancer stem cell treatment.

Lin28B/Let-7 Regulates Expression of Oct4 and Sox2 and Reprograms Oral Squamous Cell Carcinoma Cells to a Stem-like State

Lin28, a key factor for cellular reprogramming and generation of induced pluripotent stem cell (iPSC), makes a critical contribution to tumorigenicity by suppressing Let-7. However, it is unclear whether Lin28 is involved in regulating cancer stem-like cells (CSC), including in oral squamous carcinoma cells (OSCC). In this study, we demonstrate a correlation between high levels of Lin28B, Oct4, and Sox2, and a high percentage of CD44(+)ALDH1(+) CSC in OSCC. Ectopic Lin28B expression in CD44(-)ALDH1(-)/OSCC cells was sufficient to enhance Oct4/Sox2 expression and CSC properties, whereas Let7 co-overexpression effectively reversed these phenomena. We identified ARID3B and HMGA2 as downstream effectors of Lin28B/Let7 signaling in regulating endogenous Oct4 and Sox2 expression. Let7 targeted the 3' untranslated region of ARID3B and HMGA2 and suppressed their expression, whereas ARID3B and HMGA2 increased the transcription of Oct4 and Sox2, respectively, through promoter binding. Chromatin immunoprecipitation assays revealed a direct association between ARID3B and a specific ARID3B-binding sequence in the Oct4 promoter. Notably, by modulating Oct4/Sox2 expression, the Lin28B-Let7 pathway not only regulated stemness properties in OSCC but also determined the efficiency by which normal human oral keratinocytes could be reprogrammed to iPSC. Clinically, a Lin28B(high)-Let7(low) expression pattern was highly correlated with high levels of ARID3B, HMGA2, OCT4, and SOX2 expression in OSCC specimens. Taken together, our results show how Lin28B/Let7 regulates key cancer stem-like properties in oral squamous cancers.