Sofie Claerhout

Caspase-mediated cleavage of Beclin-1 inactivates Beclin-1-induced autophagy and enhances apoptosis by promoting the release of proapoptotic factors from mitochondria.

Autophagy and apoptosis are two important and interconnected stress-response mechanisms. However, the molecular interplay between these two pathways is not fully understood. To study the fate and function of autophagic proteins at the onset of apoptosis, we used a cellular model system in which autophagy precedes apoptosis. IL-3 depletion of Ba/F3 cells caused caspase (casp)-mediated cleavage of Beclin-1 and PI3KC3, two crucial components of the autophagy-inducing complex. We identified two casp cleavage sites in Beclin-1, TDVD133 and DQLD149, cleavage at which yields fragments lacking the autophagy-inducing capacity. Noteworthy, the C-terminal fragment, Beclin-1-C, localized predominantly at the mitochondria and sensitized the cells to apoptosis. Moreover, on isolated mitochondria, recombinant Beclin-1-C was able to induce the release of proapoptotic factors. These findings point to a mechanism by which casp-dependent generation of Beclin-1-C creates an amplifying loop enhancing apoptosis upon growth factor withdrawal.

Concomitant inhibition of AKT and autophagy is required for efficient cisplatin-induced apoptosis of metastatic skin carcinoma

Cutaneous squamous cell carcinoma (cSCC) is one of the most common cancers in the Caucasian population. Although early stages of skin cancer have a high curability and excellent prognosis, advanced cSCC shows resistance to chemotherapy, including cisplatin. The PI3‐K/AKT pathway is known to have a role in both skin cancer development and resistance to therapeutic drugs. In this study, we used isogenic cell lines representing different stages of malignant transformation of the keratinocytes that were derived from dysplastic forehead skin (PM1), primary cutaneous SCC (MET1) and its lymph node metastasis (MET4) of an immunosuppressed patient. We show that skin tumor progression parallels enhanced AKT activation and increased resistance to cisplatin‐induced apoptosis. Pharmacological AKT inhibition, or specific AKT1 knock down, sensitizes the apoptosis‐resistant MET1 and, to a lesser extent, MET4 cells to cisplatin‐mediated cell death. Concomitantly autophagy induction was observed in MET4, as demonstrated by accumulation of the autophagic protein marker LC3‐II, by analysis of full autophagosome maturation process using tandem mRFP‐GFP fluorescence microscopy and by electron microscopy. Counteracting the autophagic process by 3‐methyladenine or specific ATG5 knock down enhanced cytotoxicity of cisplatin combined with AKT inhibitor, thus revealing a key role for autophagy in chemoresistance. Taken together, these results indicate that concomitant inhibition of autophagy is required to increase the therapeutic benefit of AKT inhibition for combination therapy with the standard chemotherapeutic agent cisplatin in advanced skin carcinoma.

New Strategies of Photoprotection

Adequate photoprotection is essential to control UV‐related disorders, including sunburn, photoaging and photocarcinogenisis. Sun avoidance, protection of skin with clothing, and sunscreens are presently the best way of photoprotection, assuming that they are used properly. However, new strategies, which are based on or make use of the endogenous protective response to UV light, may further improve currently used photoprotective means. The addition of repair enzymes and/or antioxidants has a positive effect on skins recovery from UV‐induced DNA‐damage. Several botanical agents, mainly vitamins and polyphenols, have shown to influence signal transduction pathways leading to photo‐protective effects. Also stimulation of endogenous UV‐response pathways via irradiation with a low UV dose or via simulation of UV‐induced DNA‐damage results in photo‐protective effects. Future research in this field and combination of different photoprotective strategies will hopefully lead to improved photoprotection.

Pathways involved in sunburn cell formation: deregulation in skin cancer

The incidence of squamous cell carcinoma of the skin is rising worldwide for decades. Chronic exposure to sunlight is the most important environmental risk factor for this type of skin cancer. This is predominantly due to the DNA damaging effect of ultraviolet-B (UVB) in sunlight. UVB induces also sunburn cells, i.e. apoptotic keratinocytes, which is a crucial protective mechanism against the carcinogenic effects of UVB irradiation. This process is regulated by a wide range of molecular determinants involved in the balance between pro- and anti-apoptotic pathways. Growing evidence suggests that the deregulation of this balance by chronic UVB irradiation, contributes to the development of skin cancer. This review gives a brief summary of major known pathways involved in the regulation of keratinocyte survival and cell death upon UVB damage and discusses the contribution of the deregulation of these cascades to photocarcinogenesis.