Abstract
Hypoxia-inducible factors (HIFs) induced by reduced O2 availability activate the transcription of target genes encoding proteins that play important roles in communication between cancer and stromal cells. Cancer cells were incubated under hypoxic conditions: H1299, A549 (NSCLC); Hep3B, HepG2 (HCC); HCT116, CT26 (Colon cancer); MCF-7, MDAMB231 (Breast cancer); MKN1, MKN5 (Gastric cancer); U87MG, SHSY5Y (Brain cancer); and SKOV3, SNU840 (Ovary cancer). All cells expressed HIF-1α and HIF-2α mRNA and proteins. However, cell proliferation of NSCLC, breast, gastric, and brain cancer cells under hypoxia was more dependent on HIF-1α except for HCC cells where it was more dependent on HIF-2α. Among HIF-1α dependent cells H1299 was the most affected in terms of cell proliferation by HIF-1α knockdown. To examine which cytokines are secreted in NSCLC cells by HIF-1α to communicate with stromal cells, we performed a cytokine-profiling array with H1299. We screened the top 14 cytokines which were dependent on the HIF-1α expression pattern. Among them, midkine (MDK) expression was affected the most in response to HIF-1α. MDK is a heparin-binding growth factor that promotes angiogenesis and carcinogenesis. Indeed, MDK significantly increased HUVEV endothelial cell migration and neo- vascularization in chick chorioallantoic membrane assay (CAM) assay via paracrine signaling. In addition, MDK secreted from NSCLC cells interacted with Notch2 which activated the Notch signaling pathway and induced EMT, upregulated NF-κB, and increased cancer promotion. However, in response to MDK knock down, siRNA or the MDK inhibitor, iMDK treatment not only decreased MDK-induced migration and angiogenesis of endothelial cells but also abrogated the progression and metastasis of NSCLC cells in in vitro and in vivo orthotopic and spontaneous lung metastasis models. Consequently, iMDK treatment significantly increased mice survival rates compared with the control or MDK expression group. MDK plays a very important role in the progression and metastasis of NSCLC cells. Moreover, the MDK targeting strategy provides a potential therapeutic target for the treatment of MDK-expressing lung cancers.
Highlights
The tumor microenvironment differs from that of the normal tissue environment [1,2]
Even though it is well known that almost all cancer cells express Hypoxia-inducible factors (HIFs)-1α and HIF-2α under hypoxic conditions, HIF-2α is essential in colon cancer growth and progression among HIFs [24]
To screen which cancer cells were affected by HIF-1α or HIF-2α, we measured the protein and mRNA
Summary
The tumor microenvironment differs from that of the normal tissue environment [1,2]. The critical difference between the tumor microenvironment and that of the surrounding normal tissue is the Cancers 2020, 12, 2402; doi:10.3390/cancers12092402 www.mdpi.com/journal/cancersCancers 2020, 12, 2402 presence of intratumoral hypoxia [3]. The tumor microenvironment differs from that of the normal tissue environment [1,2]. The critical difference between the tumor microenvironment and that of the surrounding normal tissue is the Cancers 2020, 12, 2402; doi:10.3390/cancers12092402 www.mdpi.com/journal/cancers. Proteasomal degradation of the complex containing HIF-1α and HIF-1β is inhibited, and the complex is transported to the nucleus, where it binds to HIF response elements (HREs, 50 -RCGTG-30 ). The binding of the HIF complex to HREs triggers the recruitment of coactivator molecules that form transcription initiation complexes to enhance the expression of genes that mediate cellular and physiological responses to hypoxia [9]. We found that midkine (MDK) is up-regulated by hypoxia, MDK mRNA, and the expression and secretion of the protein are regulated by HIF-1α in lung cancer cells
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