James J. Driscoll

The sumoylation pathway is dysregulated in multiple myeloma and is associated with adverse patient outcome

Multiple myeloma (MM) is a plasma cell neoplasm that proceeds through a premalignant state of monoclonal gammopathy of unknown significance; however, the molecular events responsible for myelomagenesis remain uncharacterized. To identify cellular pathways deregulated in MM, we addressed that sumoylation is homologous to ubiquitination and results in the attachment of the ubiquitin-like protein Sumo onto target proteins. Sumoylation was markedly enhanced in MM patient lysates compared with normal plasma cells and expression profiling indicated a relative induction of sumoylation pathway genes. The Sumo-conjugating enzyme Ube2I, the Sumo-ligase PIAS1, and the Sumo-inducer ARF were elevated in MM patient samples and cell lines. Survival correlated with expression because 80% of patients with low UBE2I and PIAS1 were living 6 years after transplantation, whereas only 45% of patients with high expression survived 6 years. UBE2I encodes the sole Sumo-conjugating enzyme in mammalian cells and cells transfected with a dominant-negative sumoylation-deficient UBE2I mutant exhibited decreased survival after radiation exposure, impaired adhesion to bone marrow stroma cell and decreased bone marrow stroma cell-induced proliferation. UBE2I confers cells with multiple advantages to promote tumorigenesis and predicts decreased survival when combined with PIAS1. The sumoylation pathway is a novel therapeutic target with implications for existing proteasomal-based treatment strategies.

Therapeutically targeting the SUMOylation, Ubiquitination and Proteasome pathways as a novel anticancer strategy

The ubiquitin (Ub)+proteasome proteolytic pathway is responsible for the selective degradation of the majority of nuclear and cytosolic proteins. The proteasome is a high molecular weight multicatalytic protease that serves as the catalytic core of the complex Ub-dependent protein degradation pathway and is an exciting new target for the development of novel anticancer therapies. Inhibition of the proteasome, and consequently Ub-dependent proteolysis, with the small molecule pharmacologic agent bortezomib led to approval by the US Food and Drug Administration (FDA) for the treatment of multiple myeloma (MM) that has subsequently been extended to other hematologic malignancies. Inhibition of the proteasome results in the intracellular accumulation of many ubiquitinated proteins that control essential cellular functions such as cellular growth and apoptosis. The accumulation of high molecular weight Ub~protein conjugates eventually triggers apoptosis, with tumor cells more susceptible to proteasome inhibition than non-malignant cells. The defined mechanism of action for proteasome inhibitors has not been completely characterized, not all patients respond to proteasome inhibitor-based therapy, and inevitably patients develop resistance to proteasome inhibitors. Further investigation of the Ub+proteasome system (UPS) is needed to develop more effective inhibitors, to develop agents that overcome bortezomib resistance and to avoid adverse effects such as neuropathy. Furthermore, there are newly uncovered pathways, e.g., the SUMOylation and NEDDylation pathways, which similarly attach Ub-like proteins (ULPs) to protein substrates. The functional consequence of these modifications is only beginning to emerge, but these pathways have been linked to tumorigenesis and may similarly provide therapeutic targets. The immunoproteasome is a specialized form of the proteasome that produces peptides that are presented at the cell surface as major histocompatibility complex (MHC) class I antigens. Proteasome inhibitors decrease the presentation of antigenic peptides to reduce tumor cell recognition by cytotoxic T cells (CTLs) but unexpectedly increase tumor cell recognition by natural killer (NK) cells. Inhibitors of the UPS are validated, cytotoxic agents that may be further exploited in immunotherapy since they modulate tumor cell recognition by effectors of the immune system. Targeting the UPS, SUMOylation and NEDDylation pathways offers great promise in the treatment of hematologic and solid malignancies.

MicroRNA theragnostics for the clinical management of multiple myeloma

Theragnostics represent cutting-edge, multi-disciplinary strategies that combine diagnostics with therapeutics in order to generate personalized therapies that improve patient outcome. In oncology, the approach is aimed at more accurate diagnosis of cancer, optimization of patient selection to identify those most likely to benefit from a specific therapy and to generate effective therapeutics that enhance patient survival. MicroRNAs (miRNAs) are master regulators of the human genome that orchestrate myriad cellular pathways to control growth during physiologic and pathologic conditions. Compelling evidence shows that miRNA deregulation promotes events linked to tumor initiation, metastasis and drug resistance as seen in multiple myeloma (MM), an invariably fatal hematologic malignancy. miRNAs are readily detected in body fluids, for example, serum, plasma, urine, as well as circulating tumor cells to demonstrate their potential as readily accessible, non-invasive diagnostic and prognostic biomarkers and potential therapeutics. Specific miRNAs are aberrantly expressed early in myelomagenesis and may more readily detect high-risk disease than current methods. Although only recently discovered miRNAs have rapidly advanced from preclinical studies to evaluation in human clinical trials. The development of miRNA theragnostics should provide widely applicable tools for the targeted delivery of personalized medicines to improve the outcome of patients with MM.

Molecular crosstalk between the proteasome, aggresomes and autophagy: Translational potential and clinical implications

Targeting the ubiquitin+proteasome protein degradation pathway with the therapeutic agent bortezomib has significantly improved the survival of cancer patients but drug resistance inevitably develops. Aggresomes and the autophagy pathway serve as compensatory protein-clearance mechanisms that eradicate potentially toxic proteins to promote resistance to proteasome inhibitors and, hence, tumor survival. Pre-clinical evidence has emerged to demonstrate active crosstalk between these protein degradation pathways and has revealed novel therapeutic targets and strategies. Translational research and clinical trials are now focused on these pathways to prevent the emergence of drug resistance, enhance apoptosis and further improve the survival of cancer patients.

Targeting the Ubiquitin+Proteasome System in Solid Tumors

The ubiquitin+proteasome system (UPS) is a highly complex network that maintains protein homeostasis and cell viability through the selective turnover of targeted substrates. The proteasome serves as the catalytic core of the UPS to recognize and execute the coordinated and efficient removal of ubiquitinated proteins. Pharmacologic inhibitors that exploit the pivotal role of the proteasome in cellular metabolism promote tumor cytotoxicity and have yielded durable clinical responses that dramatically improve patient survival. Success of the proteasome inhibitor (PI) bortezomib in the treatment of the hematologic malignancy multiple myeloma (MM) has emerged as the standard-of-care and catapulted the UPS into a position of prominence as a model system in cancer biology and drug development. However, expansion of PIs in the treatment of the more complex solid tumors has been less successful. While clinical evaluation of second-generation PIs progresses, other potential sites of therapeutic intervention within the UPS continue to emerge, such as the non-proteolytic activities associated with the proteasome and the rapidly expanding number of Ub-binding proteins. Molecular-genetic approaches to further unravel the complexity of the UPS will advance its utilization as a platform for the development of novel, mechanism-based anticancer strategies.

Hidradenocarcinomas: a brief review and future directions.

Hidradenocarcinomas are rare, aggressive skin adnexal tumors of sweat gland origin that demonstrate a high potential for local recurrence, metastasis, and poor outcome. These neoplasms can derive from preexisting clear cell hidradenomas but more commonly appear de novo, with the molecular events responsible for the pathogenesis currently unknown. Historically, diagnosis has been difficult because of the few cases, inconsistent nomenclature, variable morphology of cells that compose the neoplasm, and confusion with other visceral metastatic tumors. Presentation is generally benign with an indolent clinical course that typically includes local and multiple recurrences. Despite wide-excision surgery, disease at regional lymph nodes and metastatic sites is common and linked to decreased survival. Currently, molecular markers of pathogenesis as well as effective forms of adjuvant chemotherapy are lacking. Future studies are required to identify the histopathologic and immunohistochemical features, which may facilitate diagnosis and foster development of molecularly targeted forms of adjuvant therapy.

The Ubiquitin+Proteasome Protein Degradation Pathway as a Therapeutic Strategy in the Treatment of Solid Tumor Malignancies

A concept that currently steers the development of cancer therapies has been that agents directed against specific proteins that facilitate tumorigenesis or maintain a malignant phenotype will have greater efficacy, less toxicity and a more sustained response relative to traditional cytotoxic chemotherapeutic agents. The clinical success of the targeted agent Imatinib mesylate as an inhibitor of the tyrosine kinase associated with the breakpoint cluster region-Abelson oncogene locus (BCR-ABL) in the treatment of Philadelphia-positive chronic myelogenous leukemia (CML) has served as a paradigm. While intellectually gratifying, the selective targeting of a single driver event by a small molecule, e.g., kinase inhibitor, to dampen a tumor-promoting pathway in the treatment of solid tumors is limited by many factors. Focus can alternatively be placed on targeting fundamental cellular processes that regulate multiple events, e.g., protein degradation, through the Ubiquitin (Ub)+Proteasome System (UPS). The UPS plays a critical role in modulating numerous cellular proteins to regulate cellular processes such as signal transduction, growth, proliferation, differentiation and apoptosis. Clinical success with the proteasome inhibitor bortezomib revolutionized treatment of B-cell lineage malignancies such as Multiple Myeloma (MM). However, many patients harbor primary resistance and do not respond to bortezomib and those that do respond inevitably develop resistance (secondary resistance). The lack of clinical efficacy of proteasome inhibitors in the treatment of solid tumors may be linked mechanistically to the resistance detected during treatment of hematologic malignancies. Potential mechanisms of resistance and means to improve the response to proteasome inhibitors in solid tumors are discussed.

Rb Suppresses Collective Invasion, Circulation and Metastasis of Breast Cancer Cells in CD44-Dependent Manner

Basal-like breast carcinomas (BLCs) present with extratumoral lymphovascular invasion, are highly metastatic, presumably through a hematogenous route, have augmented expression of CD44 oncoprotein and relatively low levels of retinoblastoma (Rb) tumor suppressor. However, the causal relation among these features is not clear. Here, we show that Rb acts as a key suppressor of multiple stages of metastatic progression. Firstly, Rb suppresses collective cell migration (CCM) and CD44-dependent formation of F-actin positive protrusions in vitro and cell-cluster based lymphovascular invasion in vivo. Secondly, Rb inhibits the release of single cancer cells and cell clusters into the hematogenous circulation and subsequent metastatic growth in lungs. Finally, CD44 expression is required for collective motility and all subsequent stages of metastatic progression initiated by loss of Rb function. Altogether, our results suggest that Rb/CD44 pathway is a crucial regulator of CCM and metastatic progression of BLCs and a promising target for anti-BLCs therapy.

Transcriptional repression of Bim by a novel YY1-RelA complex is essential for the survival and growth of Multiple Myeloma.

Abstract Multiple Myeloma (MM) is an incurable plasma cell cancer that is caused by several chromosomal translocations and gene deletions. Although deregulation of several signaling pathways including the Nuclear Factor-Kappa B (NF-κB) pathway has been reported in MM, the molecular requirement and the crosstalk between NF-κB and its target genes in MM cell survival has been largely unclear. Here, we report that Yin Yang1 (YY1), a target gene for NF-κB, is hyperexpressed in most MM tumor cells obtained from human patients, exhibits constitutive nuclear localization, and is essential for survival of MM cells. Mechanistically, we report a novel YY1-RelA complex formation, which is essential to transcriptionally repress a proapoptotic gene Bim. In line with this, depletion of YY1 or RelA resulted in elevated levels of Bim and apoptosis. Moreover, both YY1 and RelA are recruited to the Bim promoter and are required to repress the Bim promoter. Importantly, depletion of YY1 or RelA almost completely impaired the colony forming ability of MM progenitor cells suggesting that both RelA and YY1 are essential for the survival and growth of MM progenitor cells. Moreover, depletion of either YY1 or RelA completely inhibited MM tumor growth in xenograft models for human myeloma. Thus, a novel RelA-YY1 transcriptional repression complex is an attractive drug target in MM.

Targeting the Proteasome With Bortezomib in Multiple Myeloma: Update on Therapeutic Benefit as an Upfront Single Agent, Induction Regimen for Stem-Cell Transplantation and as Maintenance Therapy

Bortezomib is the first therapeutic inhibitor of the proteasome that has demonstrated a significant clinical response in patients with otherwise refractory or rapidly advancing disease. Bortezomib has received US Federal Drug Administration approval for the treatment of the hematologic malignancies such as multiple myeloma and mantle cell lymphoma. Herein, the use of bortezomib as an upfront therapy, as an induction regimen before stem-cell transplantation and as maintenance therapy in the treatment of multiple myeloma is discussed.