Hedgehog signaling regulates hypoxia induced epithelial to mesenchymal transition and invasion in pancreatic cancer cells via a ligand-independent manner

Abstract

BackgroundHypoxia plays a vital role in cancer epithelial to mesenchymal transition (EMT) and invasion. However, it is not quite clear how hypoxia may contribute to these events. Here we investigate the role of Hedgehog (Hh) signaling in hypoxia induced pancreatic cancer EMT and invasion.MethodsPancreatic cancer cells were cultured under controlled hypoxia conditions (3% O2) or normoxic conditions. HIF-1α siRNA, cyclopamine (a SMO antagonist) and GLI1 siRNA were used to inhibit HIF-1α transcription or Hh signaling activation. The effect of hypoxia and Hh signaling on cancer cell EMT and invasion were evaluated by Quantitative real-time PCR analysis, Western blot analysis and invasion assay.ResultsHere, we show that non-canonical Hh signaling is required as an important role to switch on hypoxia-induced EMT and invasion in pancreatic cancer cells. Moreover, our data demonstrate hypoxia induces EMT process as well as invasion, and activates the non-canonical Hh pathway without affecting sonic hedgehog homolog (SHH) expression. Moreover, these effects are reversible upon HIF-1α siRNA interference with unchanged SHH and patched1 (PTCH1) level. Furthermore, our data demonstrate that hypoxia induced invasion and EMT process are effectively inhibited by Smoothened (SMO) antagonist cyclopamine and GLI1 siRNA. In addition, GLI1 interference inhibited EMT progress with significantly suppressed vimentin expression, whereas inhibition of SMO through cyclopamine could not reduce vimentin level. This data indicate that hypoxia could trigger other factors (such as TGF-β, KRAS or RTK) bypassing SMO to activate GLI1 directly.ConclusionsOur findings suggest that Hh signaling modulates hypoxia induced pancreatic cancer EMT and invasion in a ligand-independent manner. Thus, Hh signaling may represent a promising therapeutic target for preventing pancreatic cancer progression.

Curcumin inhibits hypoxia-induced epithelial-mesenchymal transition in pancreatic cancer cells via suppression of the hedgehog signaling pathway

“…Sun et al (12) recently indicated that curcumin could reverse pancreatic cancer progression by inhibiting the Hh signaling pathway. The Hh signaling pathway, which is considered to play an important role in tumorigenesis, is normally quiescent in adult pancreas and has been shown to be very active in pancreatic cancer (5). Our previous study showed that hypoxia-induced invasion and EMT process is intimate related with the Hh signaling pathway (5).…”

“…Tumor hypoxia is strongly associated with enhanced tumor invasiveness, angiogenesis and distant metastasis (4). Hypoxia-inducible factor-1 (HIF-1), which belongs to the basic helix-loop-helix-periodic acidSchiff domain transcription factor family, is a key mediator of the cellular response to hypoxia and is overexpressed in a wide variety of solid tumors, including pancreatic cancer (5). Our previous study identified that the Hedgehog (Hh) signaling modulated hypoxia induced pancreatic cancer epithelial to mesenchymal transition (EMT) and invasion (5).…”

“…Hypoxia (low oxygen tension) is commonly found in solid tumors more than a few millimeters in size and is associated with a poor prognosis (4,5). Tumor hypoxia is strongly associated with enhanced tumor invasiveness, angiogenesis and distant metastasis (4).…”

A microfluidic device to study cancer metastasis under chronic and intermittent hypoxia

“…The observation of increased migration in the device with cells maintained under 1% oxygen is consistent with an extensive literature, suggesting that hypoxia generates a more aggressive phenotype 53,54 and was found in traditional transwell chamber assays for the PANC-1 cell line. [55][56][57] It should be noted that in these earlier studies, cells were trypsinized and resuspended in low-serum medium and a chemoattractant was used in each invasion assay. [55][56][57] In this communication, trypsinization, which may affect viability and invasiveness, was not necessary for the invasion assay nor was a chemoattractant (other than oxygen) added to induce migration.…”

“…[55][56][57] It should be noted that in these earlier studies, cells were trypsinized and resuspended in low-serum medium and a chemoattractant was used in each invasion assay. [55][56][57] In this communication, trypsinization, which may affect viability and invasiveness, was not necessary for the invasion assay nor was a chemoattractant (other than oxygen) added to induce migration.…”