Inhibitors of the ALK and EGF receptor tyrosine kinases provoke dramatic but short-lived responses in lung cancers harboring EML4-ALK translocations or activating mutations of EGFR, respectively. We used a large-scale RNAi screen to identify MED12, a component of the transcriptional MEDIATOR complex that is mutated in cancers, as a determinant of response to ALK and EGFR inhibitors. MED12 is in part cytoplasmic where it negatively regulates TGF-βR2 through physical interaction. MED12 suppression therefore results in activation of TGF-βR signaling, which is both necessary and sufficient for drug resistance. TGF-β signaling causes MEK/ERK activation, and consequently MED12 suppression also confers resistance to MEK and BRAF inhibitors in other cancers. MED12 loss induces an EMT-like phenotype, which is associated with chemotherapy resistance in colon cancer patients and to gefitinib in lung cancer. Inhibition of TGF-βR signaling restores drug responsiveness in MED12(KD) cells, suggesting a strategy to treat drug-resistant tumors that have lost MED12.

No abstract

The mechanisms underlying cellular drug resistance have been extensively studied, but little is known about its regulation. We have previously reported that activating transcription factor 4 (ATF4) is upregulated in cisplatinresistant cells and plays a role in cisplatin resistance. Here, we find out a novel relationship between the circadian transcription factor Clock and drug resistance. Clock drives the periodical expression of many genes that regulate hormone release, cell division, sleep-awake cycle and tumor growth. We demonstrate that ATF4 is a direct target of Clock, and that Clock is overexpressed in cisplatin-resistant cells. Furthermore, Clock expression significantly correlates with cisplatin sensitivity, and that the downregulation of either Clock or ATF4 confers sensitivity of A549 cells to cisplatin and etoposide. Notably, ATF4-overexpressing cells show multidrug resistance and marked elevation of intracellular glutathione. The microarray study reveals that genes for glutathione metabolism are generally downregulated by the knockdown of ATF4 expression. These results suggest that the Clock and ATF4 transcription system might play an important role in multidrug resistance through glutathione-dependent redox system, and also indicate that physiological potentials of Clock-controlled redox system might be important to better understand the oxidative stress-associated disorders including cancer and systemic chronotherapy.

Cancer cells show constitutive upregulation of glycolysis, and the concentration of lactate thus produced correlates with prognosis. Here, we examined whether lactate concentration and lactate transporter expression are related to migration and invasion activity. We found that the expression of the monocarboxylate transporters MCT1 and MCT4, but not MCT5, in human lung cancer cell lines was significantly correlated with invasiveness. To clarify the effects of MCT1 and MCT4 expression on invasion, we performed migration and invasion assays after transfection with siRNA specific for MCT1 or MCT4. Knockdown of MCT1 or MCT4 did not influence cell migration but reduced invasion; this was also observed for knockdown of the lactate transporter-associated protein basigin. We also demonstrated that both expression and activity of MMP9 and MMP2 were not correlated with invasion activity and not regulated by MCT1, MCT4 and basigin. Furthermore, the addition of lactate did not increase migration and invasion activity, but low concentration of 4,4¢-diisothiocyanatostilbene-2,2¢-disulphonic acid (DIDS), a general anion channel blocker, as well as other MCT inhibitors quercetin and simvastatin, inhibited cell invasion without influencing migration activity and the cellular expression of MCT1 and MCT4. This is the first report suggesting that lactate transporters are involved in human cancer cell invasiveness. As such, these proteins may be promising targets for the prevention of cancer invasion and metastasis. (Cancer Sci 2011; 102: 1007-1013 M onocarboxylates, such as lactate and pyruvate, play a central role in cellular metabolism and metabolic communication between tissues.(1) In cancer cells, a steady source of metabolic energy is required to continue the uncontrolled growth and proliferation of these cells.(2) Most cancer cells rely on a high rate of aerobic glycolysis, a phenomenon termed ''the Warburg effect'', to obtain sufficient ATP in a hypoxic microenvironment.(3) As a result of the Warburg effect, lactate is abundantly synthesized from pyruvate, (4) but lactic acid induces cellular acidosis, which triggers apoptosis. To avoid apoptosis, cancer cells must transport the lactate out of the cell. On the other hand, lactate is not just a waste product: it was recently identified as a major energy fuel in tumors.(4) Lactate is transported by monocarboxylate anion transporters (MCT; also called the solute carrier family 16 [SLC16]).(1) It is known that MCT4 (SLC16A3) transports lactate out of the cell (5) and MCT1 (SLC16A1) regulates the entry of lactate into tumor cells. (4) Migration and invasion are two of the most important aspects of the malignant cancer phenotype; if they could be inhibited, the cancer prognosis would improve. Hypoxia and acidosis create a nurturing environment for tumor progression and the evolution of metastases, and invasiveness is abetted by acidosis, the result of shifting to an anaerobic glycolytic metabolism.(6) Basigin (BSG; also called EMMPRIN and CD147) is a multifunctional glycoprotein ...

No abstract