Magnesium homeostasis in colon carcinoma LoVo cells sensitive or resistant to doxorubicin

Abstract

Neoplastic cells accumulate magnesium, an event which provides selective advantages and is frequently associated with TRPM7overexpression. Little is known about magnesium homeostasis in drug-resistant cancer cells. Therefore, we used the colon cancer LoVo cell model and compared doxorubicin-resistant to sensitive cells. In resistant cells the concentration of total magnesium is higher while its influx capacity is lower than in sensitive cells. Accordingly, resistant cells express lower amounts of the TRPM6 and 7, both involved in magnesium transport. While decreased TRPM6 levels are due to transcriptional regulation, post-transcriptional events are involved in reducing the amounts of TRPM7. Indeed, the calpain inhibitor calpeptin markedly increases the levels of TRPM7 in resistant cells. In doxorubicin-sensitive cells, silencing TRPM7 shifts the phenotype to one more similar to resistant cells, since in these cells silencing TRPM7 significantly decreases the influx of magnesium, increases its intracellular concentration and increases resistance to doxorubicin. On the other hand, calpain inhibition upregulates TRPM7, decreases intracellular magnesium and enhances the sensitivity to doxorubicin of resistant LoVo cells. We conclude that in LoVo cells drug resistance is associated with alteration of magnesium homeostasis through modulation of TRPM7. Our data suggest that TRPM7 expression may be an additional undisclosed player in chemoresistance.

The different expression of TRPM7 and MagT1 impacts on the proliferation of colon carcinoma cells sensitive or resistant to doxorubicin

“…We have previously demonstrated that TRPM7 expression is lower in confluent LoVo-R than in confluent LoVo-S, and contributes to render the cells resistant to DXR22. Here we show that the resistant phenotype is characterized not only by low amounts of TRPM7 but also by high levels of MagT1.…”

“…The role of TRPM7 in modulating LoVo cell proliferation is supported also by experiments on LoVo-R cultured in the presence of the calpain inhibitor calpeptin. The concentration of calpeptin (5 μg/ml) used in this study exerts no cytotoxic effect22. Figure 5a and b show that calpeptin upregulated TRPM7, but not MagT1 (Supplementary S5A), and induced cell proliferation.…”

“…Our results are in accordance with these findings since we show that (i) LoVo-R, which express low amounts of TRPM7, grow slower than LoVo-S; (ii) calpeptin-induced TRMP7 accelerates LoVo-R proliferation; and (iii) silencing TRPM7 hinders LoVo-S cell proliferation. We rule out that TRPM7 contributes to the regulation of cell growth by impacting on intracellular Mg since we have shown an inverse correlation between total intracellular magnesium and the levels of TRPM722. Since TRPM7 phosphorylates some proteins, we argue that silencing TRPM7 might impair the phosphorylation of its substrates.…”

“…Initially, we treated LoVo-S and -R with 2-aminoethoxydiphenyl borate (2-APB, 50 μM), a commonly used non-specific blocker of TRPM7 activity22. While no effect was observed in LoVo-R upon exposure to the compound, we found that 2-APB hindered LoVo-S cell growth (Fig.…”

“…In a recent study, we have demonstrated lower amounts of TRPM7 in LoVo-R than in LoVo-S22. Interestingly, silencing TRPM7 protects LoVo-S from the toxic effects of DXR, while calpeptin-induced upregulation of TRPM7 impairs the resistance of LoVo-R to the drug, thus indicating that TRPM7 might play a role in chemoresistance22.…”