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Background  Autophagy is a major cellular process by which cytoplasmic components such as damaged organelles and misfolded proteins are recycled. Although low levels of autophagy occur in cells under basal conditions, certain cellular stresses including nutrient depletion, DNA damage, and oxidative stress are known to robustly induce autophagy. Krüppel-like factor 4 (KLF4) is a zinc-finger transcription factor activated during oxidative stress to maintain genomic stability. Both autophagy and KLF4 play important roles in response to stress and function in tumor suppression.    Methods  To explore the role of KLF4 on autophagy in mouse embryonic fibroblasts (MEFs), we compared wild-type with  Klf4  deficient cells. To determine the levels of autophagy, we starved MEFs for different times with Earle’s balanced salts solution (EBSS). Rapamycin was used to manipulate mTOR activity and autophagy. The percentage of cells with γ-H2AX foci, a marker for DNA damage, and punctate pattern of GFP-LC3 were counted by confocal microscopy. The effects of the drug treatments,  Klf4  overexpression, or  Klf4  transient silencing on autophagy were analyzed using Western blot. Trypan Blue assay and flow cytometry were used to study cell viability and apoptosis, respectively. qPCR was also used to assay basal and the effects of  Klf4  overexpression on  Atg7  expression levels.    Results  Here our data suggested that  Klf4  −/−  MEFs exhibited impaired autophagy, which sensitized them to cell death under nutrient deprivation. Secondly, DNA damage in  Klf4 -null MEFs increased after treatment with EBSS and was correlated with increased apoptosis. Thirdly, we found that  Klf4  −/−  MEFs showed hyperactive mTOR activity. Furthermore, we demonstrated that rapamycin reduced the increased level of mTOR in  Klf4  −/−  MEFs, but did not restore the level of autophagy. Finally, re-expression of  Klf4  in  Klf4  deficient MEFs resulted in increased levels of LC3II, a marker for autophagy, and  Atg7  expression level when compared to GFP-control transfected  Klf4  −/−  MEFs.    Conclusion  Taken together, our results strongly suggest that KLF4 plays a critical role in the regulation of autophagy and suppression of mTOR activity. In addition, we showed that rapamycin decreased the level of mTOR in  Klf4  −/−  MEFs, but did not restore autophagy. This suggests that KLF4 regulates autophagy through both mTOR-dependent and independent mechanisms. Furthermore, for the first time, our findings provide novel insights into the mechanism by which KLF4 perhaps prevents DNA damage and apoptosis through activation of autophagy.    Electronic supplementary material  The online version of this article (doi:10.1186/s12943-015-0373-6) contains supplementary material, which is available to authorized users.

Impaired autophagy in mouse embryonic fibroblasts null for Krüppel-like Factor 4 promotes DNA damage and increases apoptosis upon serum starvation