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Dario C. Altieri, M.D.Academic Role: Professor
Faculty Appointment(s) In:
Other Affiliation(s):
Interface between cell survival and cell proliferation in cancer.
In particular, our laboratory studies a gene family called Inhibitors of Apoptosis (IAP). These IAP molecules have been implicated in two distinct cellular functions: preservation of mitotic transition as demonstrated in lower organisms and direct inhibition of caspases -the effector molecules of apoptosis- in mammalian cells. At least one of the mammalian members of the IAP gene family, survivin, retains the ability to participate in both functions, and has been shown by our laboratory and unanimously independently confirmed in the literature to be over-expressed in virtually every human cancer. First cloned in our laboratory, survivin is the only IAP gene that is cell cycle-regulated and prominently expressed at mitosis in a transcriptionally-controlled pathway. Upon expression in dividing cells, survivin is rapidly recruited to various aspects of the mitotic apparatus, including centrosomes, also called microtubule organizing centers, microtubules of the metaphase and anaphase spindles and midbodies at telophase. A separate nuclear pool of survivin has also been shown to localize to kinetochores of metaphase chromosomes and potentially involved in modulating chromosome dynamics and proper segregation of sister chromatids at cell division (Figure 1). Our laboratory has extensively used cell biological approaches to probe the function of survivin at cell division. For instance, interference with survivin function using molecular antagonists, including antisense, dominant negative mutants and more recently gene silencing by RNA interference unraveled multiple roles of survivin at cell division, ranging from preservation of centrosome numbers, to spindle microtubule assembly to faithful segregation of sister chromatids (Figure 2). As an example, microinjection of an antibody to survivin and analysis by time-lapse videomicroscopy, revealed that antibody interference with survivin resulted in a prolonged metaphase arrest of cervical carcinoma HeLa cells, frequently associated with onset of apoptosis. By immunofluorescence, cells injected with the antibody to survivin exhibited shortened and flattened mitotic spindles severely depleted of microtubules whereas control injected cells had bipolar spindles with a normal complement of microtubules. These data suggest that at least one of the subcellular pools of survivin is required for the assembly of a competent bipolar mitotic spindle and the proper stabilization of spindle microtubules (Figure 3). In addition to a critical role in cell division, which is also highlighted by the dramatic early embryonic lethality of survivin knockout mice, it is also clear that survivin has a function in protecting cells from apoptosis and that this pathway is exploited in nearly every human tumor. Our laboratory has used both biochemical and genetic approaches to study the role of survivin in apoptosis inhibition. Transgenic animals in which expression of survivin is directed to the skin in a tissue-specific manner exhibit strong resistance to apoptosis induced by ultraviolet B irradiation and these animals are more prone to develop aggressive skin cancers in a mouse model of chemical-induced skin carcinogenesis. Conversely, interference with survivin expression or function in tumor cells is sufficient to trigger apoptosis, to enhance the efficacy of conventional anti-tumor treatment and to exert potent anti-tumor activity in vivo. This has been shown by our laboratory and independently by several other groups using various models of human cancer in immunoincompetent mice following treatment with antisense or dominant negative survivin mutants (Figure 4). A third line of investigation in our laboratory focuses on the potential role of survivin as an interface between cell cycle progression and protection from apoptosis. Using biochemical and cell biological approaches, we have identified a critical event in survivin function that links the two properties of the molecule in cell cycle progression and regulation of apoptosis. We found that a unique Thr34 in survivin becomes phosphorylated at mitosis by the main mitotic kinase complex p34cdc2-cyclin B, also known as Cdk1. This phosphorylation event is required to enhance survivin stability at mitosis, whereas inhibition of survivin phosphorylation on Thr34 resulted in initiation of mitochondrial-dependent apoptosis, activation of the caspase cascade and strong anti-cancer activity, in various models of cancer, in vivo. Our ongoing research programs focus on the further elucidation of the checkpoint function of survivin in human cancer. Our working hypothesis is that a detailed mapping of the survivin pathway and its dual role in cell division and apoptosis control may provide a more general paradigm by which mechanisms controlling cell proliferation and cell survival come together in a single interface, and are pathways potentially exploited in human cancer. Our laboratory uses an array of experimental approaches to tackle this problem. These encompass biochemistry of protein-protein interaction of survivin/IAP-associated molecules, cell biology of microtubule dynamics and pathways of spindle formation, and genetic mimicry of survivin function in transgenic or knockout mouse models, in vivo. Our laboratory is divided in working groups addressing the various aspects of the interface between cell proliferation and cell survival and how new knowledge generated in these studies can be translated in pathophysiologically relevant approaches for cancer treatment and therapy.
Office: 428
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Our laboratory is interested in how tumor cells evade from a normal process of cellular suicide also called apoptosis or programmed cell death. It is now known that abnormally extended cell viability through inhibition of apoptosis is an invariant molecular hallmark of perhaps all human tumors, and is thought to contribute to the onset and progression of the disease by promoting the accumulation of transforming mutations and facilitating the insurgence of resistance to chemo or radiation therapy. Apoptosis is one of the most intensely investigated fields in cellular and molecular biology, and this reflects its extraordinary evolutionary conservation, its genetic complexity with multiple intersecting signaling pathways, and its critical impact on human diseases, obviously including cancer. The study of apoptosis has also provided new therapeutic opportunities for rational cancer therapy, by identifying means and pathways to lower a cellular survival threshold in cancer cells and restore their sensitivity to conventional anti-cancer drugs.
364 Plantation Street Worcester, MA 01605