ИСТИНА

Cellular senescence is considered to be a tumor suppressor program as it leads to complete inhibition of proliferation. However, tumor cells induced to senescence remain viable and develop a SASP that can contribute to inflammation and transformation of surrounding cells. Senescent cells are metabolically active, and stringent balance between synthesis and degradation of proteins is required to maintain senescent phenotype and viability. The present work was performed using E1A+cHa-Ras transformed fibroblasts. It is known that Ras/Raf/MEK/ERK cascade contributes to activation of mTOR kinase – a key regulator of cellular senescence. We have studied involvement of MEK/ERK pathway in development of senescent phenotype and in regulation of cell viability of Ras-transformed cells induced to senescence by HDACi sodium butyrate (NaBut). PD0325901 (PD) was used to inhibit MEK/ERK pathway. We showed that when senescence is induced upon suppressed MEK/ERK pathway, such markers of senescence as cell cycle arrest, SA-beta-galactosidase activity, cell size and protein content and levels of lactate are reduced in comparison with NaBut treatment alone. Despite ERK1,2 inhibition, the level of mTOR Complex 1 activity remains high, preventing complete decrease of senescence markers expression. However, mTORC1 activity fails to maintain cellular viability, and NaBut + PD treated cells die due to massive cell death. In NaBut + PD-treated cells mitochondria undergo destruction of their internal structure without damage of outer membranes, thereby they are not removed by mitophagy. In cells treated with PD alone activation of AMPK favors AMPK-mediated autophagy and helps Ras-transformed cells to overcome treatment with PD. In NaBut + PD-treated cells, which have a high level of mTORC1 activity and mitochondrial dysfunction, activation of AMPK leads to a change in metabolic homeostasis that is essential for viability of senescent cells. Thus, we show that inhibition of MEK/ERK pathway in cells induced to senescence activates form of autophagy that is unable to restore the energy deficit and apparently destroys the complicated metabolic balance, which supports of viability of Ras-transformed senescent cells. This work was supported by Russian Scientific Foundation № 14-50-00068