The hypoxia-mimetic agent CoCl2 induces chemotherapy resistance in LOVO colorectal cancer cells

Abstract

Hypoxia, which is an important factor that mediates tumor progression and poor treatment response, is particularly associated with tumor chemoresistance. However, the molecular mechanisms underlying hypoxia-induced colorectal cancer chemoresistance remain unclear. The present study aimed to explore the mechanism underlying hypoxia-induced chemotherapy resistance in LOVO colorectal cancer cells. LOVO cells were cultured in a hypoxic environment simulated by cobalt chloride (CoCl2), which is a chemical inducer of hypoxia-inducible factor-1α (HIF-1α). HIF-1α is a transcription factor that has an important role in tumor cell adaptation to hypoxia, and controls the expression of several genes. Various CoCl2 concentrations are often used to simulate degrees of hypoxia. In the present study, following treatment with CoCl2, an MTT assay was conducted to determine the growth and drug sensitivity of LOVO cells. Reverse transcription-polymerase chain reaction and western blotting were used to detect the mRNA and protein expression levels of HIF-1α and factors associated with chemotherapy resistance, including multidrug resistance protein (MRP) and multidrug resistant 1 (MDR1), which encodes the major transmembrane efflux transporter P-glycoprotein (P-gp). In addition, the expression levels of apoptosis-related proteins, including B-cell lymphoma 2 (Bcl-2), Bcl-2-associated X protein (Bax) and Bcl-2-associated agonist of cell death (Bad) were detected by western blotting. Flow cytometry (FCM) was used to visually observe Adriamycin (ADR) accumulation and retention, thus analyzing intracellular drug transportation in cells under hypoxic and normoxic conditions. CoCl2-simulated hypoxia was able to inhibit tumor cell proliferation, and upregulate the expression levels of HIF-1α, MDR1/P-gp and MRP. In addition, proapoptotic members of the Bcl-2 protein family, Bax and Bad, were downregulated. The anti-apoptotic member Bcl-2 exhibited no significant change in expression, whereas the ratio of Bcl-2/Bax was increased. Results of FCM demonstrated that the intracellular retention of ADR was significantly decreased in the hypoxia group cells. In conclusion, the present study revealed that a CoCl2-simulated hypoxic microenvironment was able to effectively induce chemoresistance and reduce apoptosis in LOVO cells.

Baclofen Protects Primary Rat Retinal Ganglion Cells from Chemical Hypoxia-Induced Apoptosis Through the Akt and PERK Pathways

“…While it is difficult to control oxygen levels precisely to simulate hypoxic condition in cell culture, various in vitro models of neuronal hypoxia have been provided using divalent cations such as cobalt (Montel et al, 2007; Hang et al, 2009; Lopez-Sánchez et al, 2014; Yang et al, 2016). Cobalt have been applicable to mimic hypoxic conditions in cultured cells because they activate hypoxic signals by stabilizing the expression of hypoxia-inducible factor-1 alpha (HIF-1α), an O 2 -regulated transcriptional activator.…”

Tumor stressors induce two mechanisms of intracellular P-glycoprotein–mediated resistance that are overcome by lysosomal-targeted thiosemicarbazones

“…Moreover, the effect was more pronounced under hypoxia. This would agree with previous studies suggesting the role of HIF-1α in Pgp expression (5)(6)(7). Considering this, to directly examine the role of HIF-1α in Pgp upregulation after exposure to microenvironmental stressors, HIF-1α was silenced using siHIF-1α relative to the non-targeting control (siNC) in KBV1 (+Pgp) cells (Fig.…”

“…Furthermore, we demonstrate that stressors characteristic of the tumor micro-environment greatly affected drug resistance not only by upregulating Pgp, but also by re-localizing Pgp to lysosomes. This investigation also showed that stressors up-regulate HIF-1α, which is involved in the transcriptional up-regulation of Pgp (5)(6)(7)32).…”

“…Transporter, Pgp -Our studies initially assessed: (1) the effect of micro-environmental stressors on Pgp expression; and (2) the effect of these stressors on HIF-1α, a stress-activated transcription factor involved in Pgp expression (5)(6)(7). Classical tumor micro-environmental stressors assessed included: hypoxia (1% O2), glucose starvation (0 µM; (-) glucose), serum starvation ((-) serum), or H2O2 stress (100 μM; (+) H2O2) (12,25,26).…”

Local Delivery of β-Elemene Improves Locomotor Functional Recovery by Alleviating Endoplasmic Reticulum Stress and Reducing Neuronal Apoptosis in Rats with Spinal Cord Injury

“…Moreover, caspase 12 as a key protein activated by ER stress eventually activates caspase 3 to induce the cellular apoptosis. Cobalt is appropriate for mimicking hypoxic conditions in cultured cells due to its ability to activate hypoxic signals by stabilizing the expression of hypoxia-inducible factor-1 alpha [42,43]. Thus, CoCl 2 was used to mimic hypoxic conditions in VSC4.1 motor neurons.…”