Apoptosis and in situ and invasive squamous cell carcinoma in sun-exposed sites

In vitro evidence indicates that the E6 protein of human papillomavirus (HPV) targets Bak, a proapoptotic protein, expression of which is enhanced in epidermal keratinocytes in response to ultraviolet B radiation. Given this, our aim was to ascertain Bak expression and prevalence of beta-HPV (β-HPV) in cutaneous squamous cell carcinoma (SCC) from sun-exposed sites to test our hypothesis that the virus plays a role in the neoplastic process by suppressing UV-induced apoptosis. This retrospective study included 30 cases of cutaneous SCC and 30 cases of SCC in situ (SCCIS) from sun-exposed sites. Immunohistochemical staining for Bak protein was performed on all, and β-HPV subtyping on 10 randomly selected cases from each group, using a broad-spectrum polymerase chain reaction-reverse hybridization assay. A semiquantitative scoring system for immunohistochemical expression of Bak was used based on the percentage positivity of the cells. Of cases studied, 30 of 30 (100%) of SCCIS and SCC (mean score 4.2 and 4.6, respectively, demonstrated immunopositivity, albeit to varying degrees, with Bak. Of the selected cases studied with reverse hybridization assay, 7 of 10 (70%) of SCCIS and 3 of 10 (30%) of SCC had β-HPV with HPV-5 being the most common subtype detected. Enhanced Bak immunoexpression confirms the presence of UV-induced apoptosis in both in situ as well as invasive epithelial malignancies, although the lack of differences in expression of Bak between both groups studied suggests that its relevance in disease progression is minimal. Expression of Bak in 100% of HPV-containing lesions from sun-exposed sites suggests that the virus does not abrogate UV-induced apoptosis.

Apoptosis, P53 and Bcl-2 expression in response to topical calcipotriol therapy for psoriasis

BACKGROUND

The histopathologic changes characteristic of psoriasis might be related to suppressed apoptosis. The P53 and Bcl-2 proteins play a central role in the regulation of apoptosis. This study aimed to evaluate P53 and Bcl-2 expression and apoptotic cells in the psoriatic skin before and after topical calcipotriol therapy.

METHODS

Skin biopsies were obtained from nonlesional and lesional skin of 10 patients with generalized plaque psoriasis before and after treatment with topical calcipotriol ointment. The P53 and Bcl-2 expression was evaluated using immunoperoxidase technique and apoptotic cells by the terminal deoxynucleotide transferase (TdT) mediated deoxyuridine triphosphate nick end labeling (TUNEL) method.

RESULTS

After topical calcipotriol therapy, keratinocytes of psoriatic skin showed significant decrease of P53 (P = 0.002) and increase of Bcl-2 (P = 0.01) expression. On the other hand lymphocytes showed significant decrease of Bcl-2 (P = 0.01). There were no apoptotic cells before treatment but after calcipotriol therapy, apoptosis was more detectable in keratinocytes than in lymphocytes.

CONCLUSIONS

The results of the study suggested that one of the actions of calcipotriol in psoriasis might be exerted through induction of apoptosis, especially of keratinocytes, through a P53-independent pathway. Meanwhile, suppression of Bcl-2 expression in lymphocytes may promote apoptosis of dermal lymphocytes leading to healing of psoriasis.

Overexpression of bcl-2 in lymphocytes of psoriatic skin

Bcl-2 overexpression in lymphocytes play an important part in immunological and inflammatory diseases. In the present study, we investigated the bcl-2 expression in dermal lymphocytes of psoriatic skin biopsy samples. From the archives of the Department of Pathology, Ondokuz Mayis University Medical School (Samsun, Turkey), tissue sections belonging to 28 psoriasis cases and 10 chronic non-specific inflammatory skin disease cases were immunohistochemically stained by bcl-2. Positive staining was semiquantitatively graded from 1+ to 4+. Of the 28 psoriasis cases 20 were found to express bcl-2. Our data suggest that bcl-2-mediated inflammation plays a part in the pathogenesis and recurrent character of psoriasis.

Role of Bak in UV-induced apoptosis in skin cancer and abrogation by HPV E6 proteins

Ultraviolet B (UVB) damage is recognized as the most important etiological factor in the development of skin cancer. Human papillomaviruses (HPV) have also been implicated in the disease, although the mechanism of action of these viruses remains unknown. We present evidence here that Bak protein is involved in signaling apoptosis in the skin in response to UVB damage, and that cutaneous HPV E6 proteins target and abrogate Bak function by promoting its proteolytic degradation both in vitro and in regenerated epithelium. Additionally, HPV positive skin cancers had undetectable levels of Bak in contrast to HPV negative cancers, which expressed Bak. This study supports a link between the virus and UVB in the induction of HPV-associated skin cancer and reveals a survival mechanism of virally infected cells.