Stearoyl-CoA desaturase-1 promotes colorectal cancer metastasis in response to glucose by suppressing PTEN

Abstract

Background: Diabetic patients have a higher risk factor for colorectal cancer (CRC) metastasis. Stearoyl-CoA desaturase 1 (SCD1), the main enzyme responsible for producing monounsaturated fatty acids(MUFA) from saturated fatty acids, is frequently deregulated in both diabetes and CRC. The function and mechanism of SCD1 in metastasis of CRC and its relevance to glucose remains largely unknown.

Methods: SCD1 expression levels were analyzed in human CRC tissues and the Cancer Browser database ( https://genome-cancer.ucsc.edu/ ). CRC cell lines stably transfected with SCD1 shRNAs or vector were established to investigate the role of SCD1 in modulating migration and invasion of CRC cells. A glucose concentration gradient was set to investigate regulation of SCD1 in CRC relevant to diabetic conditions.

Results: The clinical data analysis showed high expression of SCD1 in CRC tissues with a negative correlation with the prognosis of CRC. In vitro experiments revealed that SCD1 increased CRC progression through promoting epithelial-mesenchymal transition (EMT). Lipidomic analysis demonstrated that SCD1 increased MUFA levels and MUFA administration could rescue migration and invasion defect of CRC cells induced by SCD1 knockdown. Furthermore, SCD1-mediated progression of CRC was promoted by carbohydrate response-element binding protein (ChREBP) in response to high glucose. Mechanistically, hyperglycemia-SCD1-MUFA induced CRC cell migration and invasion by regulating PTEN.

Conclusions: Our findings show that SCD1 promotes metastasis of CRC cells through MUFA production and suppressing PTEN in response to glucose, which may be a novel mechanism for diabetes-induced CRC metastasis.

Keywords: ChREBP; Colorectal cancer; High glucose; Metastasis; PTEN; SCD1.

Fig. 1

SCD1 is upregulated in human CRC tissues and associated with CRC prognosis. a SCD1 mRNA level in colorectal cancer tissues (CRC) and matched adjacent non-tumor tissues (Control) detected by Real Time-PCR. b Representative Western blot and quantification data of SCD1 and EMT markers (E-cadherin and vimentin) in colorectal cancer tissue and matched adjacent non-tumor tissue. c Representative images of immunohistochemmical staining of SCD1 and Ki67 in human cancer tissues and normal tissues (400×). The scale bar is 50 μm. d The overall survival (OS) rate of CRC patients with different SCD1 expression levels. e The relevance of SCD1 expression level to cancer stages of CRC patients

Fig. 2

SCD1 promotes migration and invasion of colorectal cancer cells by regulating EMT. a Representative Western blot of SCD1 and quantification result in five colorectal cancer cell lines. b Protein levels of SCD1 in HCT116 cells transfected with shRNAs for SCD1 (sh1 and sh2) or Caco2 cells ectopically expressing SCD1. c Transwell assay of HCT116 cells after SCD1 knockdown. The scale bar is 100 μm. d, e Histograms show the numbers of migrated (d) and invasive (e) HCT116 cells. f Transwell assay of Caco2 cell lines after SCD1 overexpression. The scale bar is 100 μm. g Histograms show the numbers of migrated and invasive Caco2 cells. h Morphological analysis of lung metastasis in mice injected with HCT116 cells transfected with control shRNA or SCD1 shRNA (n = 8 per group). Arrows indicate metastatic nodules in the lungs. The scale bar is 200 μm. i, j Protein levels of E-cadherin and vimentin in colorectal cancer cells transfected with SCD1 shRNA (i) or SCD1 cDNA (j)

Fig. 3

Lipidomics analysis for HCT116 cells transfected with shSCD1 or shNC. a Volcano plots show log2 fold-changes versus −log10 P-values of lipid species of HCT116 transfected with shSCD1 when compared with control cells. The horizontal line indicates the cut-off value for significance levels. Each dot represents a lipid species (red: lipid species P < 0.05 with a > 2 fold-change; grey: not significant). b-d Relative abundance of lipids extracted from shSCD1 or shNC-transfected HCT116 cells, including PE (b), MG (c) and TG (d)

Fig. 4

Effect of OA on migration and invasion ability of CRC cells. a Representative photographs of transwell assays of Caco2 cells after OA or BSA treatment for 48 h. The scale bar is 100 μm. b-c Histograms show the numbers of migrated (b) and invasive Caco2 cells (c). d-e Representative photographs of transwell assays of shSCD1 or shNC-transfected HCT116 (d) and SW116 (e) cells after 0.1 mM OA or BSA treatment. The scale bar is 100 μm. f-g Histograms show the numbers of migrated cells (f) and invasive cells (g)

Fig. 5

Hyperglycemia promotes SCD1 expression as well as migration and invasion of CRC cells. a, b) IPGTT (a) and ITT (b) of chow-fed and HFD-fed mice. c Representative Western blot and quantified results of SCD1 and ChREBP in colon tissues from chow and HFD fed mice. d, e HCT116 cells treated with glucose for 24 h and expression levels of SCD1 and ChREBP were determined by Real Time-PCR (d) and Western blot (e). f Transwell assay of HCT116 cells treated with 0 mM (G0), 5.5 mM (G5.5), 11 mM (G11) or 25 mM (G25) glucose. The scale bar is 100 μm. g, h) Histograms show the numbers of migrated cells (g) and invasive cells (h) under different glucose conditions

Fig. 6

SCD1 contributes to glucose-induced migration and invasion of colorectal cancer cells. a Representative photographs of transwell assays of shSCD1 or shNC-transfected HCT116 cells after glucose treatment. The scale bar is 100 μm. b, c) Histograms show the numbers of migrated (b) and invasive (c) HCT116 cells. d Representative photographs of transwell assays of Caco2 cells ectopically expressing NC or SCD1 after glucose treatment. The scale bar is 100 μm. e, f Histograms show the numbers of migrated (e) and invasive Caco2 cells (f)

Fig. 7

PTEN plays an important role in SCD1-induced migration and invasion of CRC cells. a, b Representative Western blot and quantification data of PTEN proteins of OA-treated HCT116 (a) and Caco2 (b) cells. c Representative Western blot and quantification data of PTEN in HCT116 cells transfected with siRNAs for PTEN (si1 and si2) or Caco2 cells ectopically expressing PTEN. d Representative photographs of transwell assays of shSCD1 or shNC-transfected HCT116 after being transfected with PTEN siRNAs (siPTEN) or negative control scramble siRNAs (siNC). The scale bar is 100 μm. e, f Histograms show the numbers of migrated (e) and invasive (f) HCT116 cells. g Transwell assay of SCD1 overexpression Caco2 cell lines after ectopically expressing PTEN. The scale bar is 100 μm. h, i Histograms show the number of migrated (h) and invasive (i) Caco2 cells

Fig. 8

Schematic diagram describing the functional significance of SCD1 in glucose-induced progression of CRC. SCD1 contributes to glucose-induced migration and invasion of CRC by increasing MUFA production to inhibit PTEN