Differential responses of Mcl-1 in photosensitized epithelial vs lymphoid-derived human cancer cells

Squamous cell carcinomas (SCCs) are associated with ultraviolet radiation and multiple genetic changes, but the mechanisms leading to genetic instability are unclear. SCC cell lines were compared to normal keratinocytes for sensitivity to ultraviolet radiation, DNA repair kinetics and DNA repair protein expression. Relative to normal keratinocytes, four SCC cell lines were all variably sensitive to ultraviolet radiation and, except for the SCC25 cell line, were deficient in global repair of cyclobutane pyrimidine dimers, although not 6-4 photoproducts. Impaired DNA repair of cyclobutane pyrimidine dimers was associated with reduced mRNA expression from XPC but not DDB2 genes which each encode key DNA damage recognition proteins. However, levels of XPC or DDB2 proteins or both were variably reduced in repair-deficient SCC cell lines. p53 levels did not correlate with DNA repair activity or with XPC and DDB2 levels, but p63 levels were deficient in cell lines with reduced global repair. Repair-proficient SCC25 cells depleted of p63 lost XPC expression, early global DNA repair activity and UV resistance. These results demonstrate that some SCC cell lines are deficient in global nucleotide excision repair and support a role for p63 as a regulator of nucleotide excision repair in SCCs.

Section: Discussionmentioning

confidence: 52%

Deficient Nucleotide Excision Repair in Squamous Cell Carcinoma Cells

Dong

Ona

Scandurra

et al. 2016

“…We have recently reported that another antiapoptotic homolog of Bcl‐2, Mcl‐1, behaves differently from either Bcl‐2 or Bcl‐xL in response to Pc 4‐PDT (29). We found no evidence of prompt photodamage to Mcl‐1 in any of the cell lines studied, including A431 and Jurkat, in spite of the localization of this protein, at least in part, to the mitochondria and endoplasmic reticulum.…”

Section: Resultsmentioning

confidence: 99%

Apoptosis Mechanisms Related to the Increased Sensitivity of Jurkat T‐cells vs A431 Epidermoid Cells to Photodynamic Therapy with the Phthalocyanine Pc 4^†‡

Ke¹,

Xue²,

Feyes³

et al. 2008

Self Cite

To examine the clinical applicability of Pc 4, a promising second-generation photosensitizer, for the photodynamic treatment of lymphocyte-mediated skin diseases, we studied the A431 and Jurkat cell lines, commonly used as surrogates for human keratinocyte-derived carcinomas and lymphocytes, respectively. As revealed by ethyl acetate extraction and absorption spectrophotometry, uptake of Pc 4 into the two cell lines was linear with Pc 4 concentration and similar on a per cell basis but greater in Jurkat cells on a per mass basis. Flow cytometry showed that uptake was linear at low doses; variations in the dose-response for uptake measured by fluorescence supported differential aggregation of Pc 4 in the two cell types. As detected by confocal microscopy, Pc 4 localized to mitochondria and endoplasmic reticulum in both cell lines. Jurkat cells were much more sensitive to the lethal effects of phthalocyanine photodynamic therapy (Pc 4-PDT) than were A431 cells, as measured by a tetrazolium dye reduction assay, and more readily underwent morphological apoptosis. In a search for molecular factors to explain the greater photosensitivity of Jurkat cells, the fate of important Bcl-2 family members was monitored. Jurkat cells were more sensitive to the induction of immediate photodamage to Bcl-2, but the difference was insufficient to account fully for their greater sensitivity. The antiapoptotic protein Mcl-1 was extensively cleaved in a dose- and caspase-dependent manner in Jurkat, but not in A431, cells exposed to Pc 4-PDT. Thus, the greater killing by Pc 4-PDT in Jurkat compared with A431 cells correlated with greater Bcl-2 photodamage and more strongly to the more extensive Mcl-1 degradation. Pc 4-PDT may offer therapeutic advantages in targeting inflammatory cells over normal keratinocytes in the treatment of T-cell-mediated skin diseases, such as cutaneous lymphomas, dermatitis, lichenoid tissue reactions and psoriasis, and it will be instructive to evaluate the role of Bcl-2 family proteins, especially Mcl-1, in the therapeutic response.

“…The role of these proteins in PDT efficacy is not entirely clear. Oleinick’s group has shown that caspase‐induced cleavage of Mcl‐1 can result in the appearance of a proapoptotic fragment (10) that enhances the apoptotic response.…”

Section: Resultsmentioning

confidence: 99%

Promotion of PDT Efficacy by a Bcl‐2 Antagonist

Kessel¹

2007

Photodynamic therapy (PDT) directed against the endoplasmic reticulum (ER) is also known to target antiapoptotic Bcl-2 family proteins. This effect is associated with the initiation of both apoptosis, a cell death pathway, and autophagy, an organelle recycling system that can lead to survival or cell death. In this study, we examined the ability of the Bcl-2 antagonist HA14-1 to promote the photodynamic efficacy of PDT directed at the ER. At concentrations that independently caused only a small loss of viability, HA14-1 markedly enhanced the proapoptotic and phototoxic effects of ER photodamage. These results provide additional evidence that the antiapoptotic properties of Bcl-2 constitute an important determinant of photokilling, and demonstrate that synergistic effects can result when PDT is coupled with pharmacologic suppression of Bcl-2 function.