Molecular mechanisms of chromium(VI)-induced apoptosis and malignant transformation

Hexavalent chromium [Cr(VI)] compounds are redox cycling environmental carcinogens that induce apoptosis as the primary mode of cell death. Apoptosis is abnormally regulated in various disorders including cancer. Therefore, to understand the etiologies of these diseases, it is important to delineate the biochemical and molecular pathways involved in the regulation of apoptosis. The main objective of this study was to characterize the molecular mechanisms involved in Cr(VI)-induced apoptosis and malignant transformation. We found that both death receptor and mitochondrial pathways of apoptosis are involved in Cr(VI)-induced apoptosis, with the latter being more dominant. Consequently, overexpression of the mitochondrial anti-apoptotic protein Bcl-2 blocked Cr(VI)-induced apoptosis in human lung epithelial cells. We further observed that reactive oxygen species (ROS) play a critical role in Cr(VI)-induced apoptosis by acting through the mitochondrial death pathway. Superoxide anion (˙O2 -) was found to be the major ROS involved in Cr(VI)-induced apoptosis that exerted its effect by degrading Bcl-2 protein through the ubiquitin-proteasomal pathway. Furthermore, nitric oxide (NO) scavenged ˙O2 - to form peroxynitrite (ONOO-) and negatively regulated Cr(VI)-induced apoptosis. The mechanism by which NO exerted its anti-apoptotic effect involved upregulation of Bcl-2 via S-nitrosylation that prevented its ubiquitination and subsequent proteasomal degradation. Additionally, we established an in vitro model for studying Cr(VI)-induced malignant transformation by subjecting non-tumorigenic human lung epithelial Beas-2B cell line to long-term Cr(VI) exposure. Cr(VI) transformed cells exhibited clear signs of malignancy such as loss of contact inhibition and increased colony formation as compared to the passage-matched original cell-line. Cr(VI) transformed cells showed decreased apoptosis and ROS production and increased NO as well as Bcl-2 expression. These observations confirmed that NO mediated stabilization of Bcl-2 is an important event in Cr(VI) induced carcinogenesis. Taken together, our study reveals a novel regulatory mechanism that could be important in apoptosis resistance in response to Cr(VI) exposure. Additionally, this study demonstrated Cr(VI)-induced malignant transformation of a human lung epithelial cell line, establishing an important in vitro model for studying the molecular mechanisms involved in Cr(VI)-induced carcinogenesis. This study provides new mechanistic insights about environmental carcinogen induced human lung cancer. Since Cr(VI) is a paradigm of carcinogenic transition metals, the inferences from this study may be broadly applied to general metal carcinogenesis

Chemoresistance of Lung Cancer Cells: 2D and 3D In Vitro Models for Anticancer Drug Screening

Chemoresistance of lung cancer cells is a key factor that limits the treatment of lung cancer patients. Patients may initially respond to standard chemotherapy, but this is often followed by rapid development of drug resistance and disease progression. Tumor heterogeneity and the presence of putative cancer stem-like cells (CS-LCs) provide a viable explanation for the chemoresistance of several types of tumors. In this book chapter, we will first describe the current knowledge of the role of both tumor heterogeneity and CS-LCs in lung cancer chemoresistance, tumor progression and metastasis. Next, we will discuss ongoing strategies at the in vitro level to screen for more effective anticancer drugs. We will specifically focus in three-dimensional (3D) culture systems (Spheroids and tumorspheres) and their application in anticancer drug discovery for lung cancer

Leadership and Management Are One and the Same

Defining the attributes of change catalysts within high functioning organizations, including the academic enterprise, is desirable. An understanding of these attributes within our academy may foster faculty interest and engagement in seeking administrative roles and serve to bolster succession planning within our schools. On one hand, there have been numerous publications teasing out the purported differences between leadership and management. On the other hand, does segregating these important characteristics based upon arbitrary distinctions do more harm than good? This commentary represents the work of a group of academic leaders participating in the 2015-2016 AACP Academic Leadership Fellowship Program. This work was presented as a debate at the 2016 AACP Interim Meeting in Tampa, Florida, in February 2016

Cyto-histological correlation of salivary gland lesions- a prospective study in a tertiary care institute

Background: Fine needle aspiration cytology (FNAC) has an essential proven role in diagnosing most of the common and benign salivary gland lesions. However, limited cellularity and morphological heterogeneity of the lesion can pose diagnostic challenges. The present study was conducted in a tertiary care centre over a period of one year with an objective to study the cyto-morphological features of salivary gland lesions and correlate cytological findings with histopathology.Methods: The study was carried out over a period of one year from January 2014 to December 2014. FNA specimens obtained from 78 patients were analyzed. Of these, only 51 patients underwent biopsy or surgery and their specimens were subjected to histopathological examination. Validation of cytological diagnosis was done on the basis of histopathological diagnosis.Results: A total 78 patients with salivary gland lesions were subjected to FNAC. Non neoplastic lesions constituted 19 cases (25%) and benign lesions constituted 46 cases (80.70%).  Malignant lesions constituted 11 cases (19.30%). Two cases were inconclusive due to inadequate aspirated material. Overall sensitivity, specificity and diagnostic accuracy were 95.98%, 99.20% and 98.09% respectively.Conclusions: FNAC continues to be an accurate diagnostic technique in the hands of an experienced cytopathologist. It is a highly sensitive and specific technique for rapid diagnosis of most of the salivary gland swellings

Multifunctional Role of Bcl-2 in Malignant Transformation and Tumorigenesis of Cr(VI)-Transformed Lung Cells

B-cell lymphoma-2 (Bcl-2) is an antiapoptotic protein known to be important in the regulation of apoptosis in various cell types. However, its role in malignant transformation and tumorigenesis of human lung cells is not well understood. We previously reported that chronic exposure of human lung epithelial cells to the carcinogenic hexavalent chromium Cr(VI) caused malignant transformation and Bcl-2 upregulation; however, the role of Bcl-2 in the transformation is unclear. Using a gene silencing approach, we showed that Bcl-2 plays an important role in the malignant properties of Cr(VI)-transformed cells. Downregulation of Bcl-2 inhibited the invasive and proliferative properties of the cells as well as their colony forming and angiogenic activities, which are upregulated in the transformed cells as compared to control cells. Furthermore, animal studies showed the inhibitory effect of Bcl-2 knockdown on the tumorigenesis of Cr(VI)-transformed cells. The role of Bcl-2 in malignant transformation and tumorigenesis was confirmed by gene silencing experiments using human lung carcinoma NCI-H460 cells. These cells exhibited aggressive malignant phenotypes similar to those of Cr(VI)-transformed cells. Knockdown of Bcl-2 in the H460 cells inhibited malignant and tumorigenic properties of the cells, indicating the general role of Bcl-2 in human lung tumorigenesis. Ingenuity Pathways Analysis (IPA) revealed potential effectors of Bcl-2 in tumorigenesis regulation. Additionally, using IPA together with ectopic expression of p53, we show p53 as an upstream regulator of Bcl-2 in Cr(VI)-transformed cells. Together, our results indicate the novel and multifunctional role of Bcl-2 in malignant transformation and tumorigenesis of human lung epithelial cells chronically exposed to Cr(VI)