research

The Blenis lab concentrates on the regulation of several signaling mechanisms inside a single cell, hoping to decipher the cell's complex internal code. These signaling processes regulate basic metabolic processes, translation, transcription, cell motility, cell growth, cell proliferation, cell differentiation, cell survival and cell death. Eventually, we hope to be able to offer highly specific drugs that could interfere with the process of a cell's becoming malignant or otherwise taking the wrong path.

Project Descriptions

Phosphorylation of a protein kinase can modulate its activity, change it cellular location and/or temporally alter its signal output. If one of the substrates of a kinase is itself another kinase, a cascade of protein phosphorylation can be initiated, leading to signal amplification and transduction. We have focused on understanding how several protein phosphorylation cascades are regulated during cell growth and proliferation, differentiation, cell survival, death and in a variety of human diseases. Ultimately, this knowledge should lead to the rational design of reagents for use in specifically antagonizing these signaling processes. Such "drugs" may be useful in the treatment of neoplasms, immune system disorders, and many others diseases associated with improper regulation of cell proliferation.

Mitogenic/Oncogenic Signaling via Ras and the ERK-MAP kinase/RSK pathway.

Activation of cell surface and cytosolic receptors with growth factors, cytokines, hormones, tumor promoting phorbol esters or the proto-oncoprotein Ras, results in activation of the Mitogen-Activated Protein Kinases (or ERK-MAPKs) and the ERK-regulated kinases (or RSKs). Signaling by these protein kinases alters the activity and/or cellular distribution of several proteins that regulate immediate-early gene expression, cell adhesion and motility, cell proliferation, differentiation, and cell survival. Although the backbone for this signaling cascade has been defined (fig.1, animated PowerPoint slide), critical details regarding its regulation remain unclear. We are utilizing a variety of biochemical, cell biological and RNAi-based approaches to characterize the molecular basis for RSK activation and signaling (fig.2, animated PowerPoint slide), the temporal regulation and spatial distribution of ERK and RSK and how this translates into a cell context-specific response (fig.3, animated PowerPoint slide), what regulates the membrane, cytoplasmic and nuclear shuttling of these kinases, and how they regulate immediate-early and delayed-response gene expression. How these G0/G1 signaling systems communicate with the G1 cell cycle machinery is also being investigated. Finally, novel protein kinases that participate in Ras signaling are being characterized and their role in normal and transformed cell proliferation is being investigated. For a review on ERK, RSK and survival signaling see Ballif and Blenis (2001) (PDF). For an extensive review on RSK and other MAP kinase-regulated kinases (MKs) see the review by Roux and Blenis (PDF).

Mitogenic/Oncogenic Signaling via PI3-kinase, mTOR and the S6 protein kinase/eIF-4E protein translation pathway.

Phosphatidylinositol 3-kinase (PI3K) signaling plays an important role in regulating protein translation, cell size/growth, G1 cell cycle progression, and cell survival through the Rho family G proteins, the translation initiation factor eIF4E and many PI3K-effector kinases like PDK1, Akt, PKCzeta, and the S6 kinases, PI3K is activated by a variety of growth factors and cytokines and is constitutively activated by loss of function/expression of the tumor suppressor PTEN, which occurs in greater than 30% of human cancers. The molecular basis of S6K activation (fig.4, animated PowerPoint slide) and eIF4E regulation by PI3K inputs, and downstream signaling by these effectors including their role in mRNA processing/translation and ribosome biogenesis, and their contribution to tumorigenesis, is currently being examined. For an extensive description of S6K regulation see the review by Martin and Blenis (PDF).

Integration of signaling by nutrients, energy sufficiency and growth factors.

The importance of nutrient/energy signaling has recently become clear with the demonstration that tumor suppressors mutated in diseases such as tuberous sclerosis (TSC1/2) or Peutz-Jeghers syndrome (LKB1) regulate signaling to the nutrient sensor, mTOR. This protein kinase is activated by the G protein Rheb, and is specifically inhibited by the drug rapamycin, an FDA approved immunosuppressant and inhibitor of restenosis. Rapamycin is also currently in clinical trials for a variety of cancers. How nutrients such as branched-chain amino acids or energy sufficiency signal to mTOR, and how mitogenic signals and nutrient signals collaborate to regulate S6 kinases and eIF4E is currently under investigation (fig.5, animated PowerPoint slide). Comprehensive reviews on mTOR and PI3K signaling have recently been published by Richardson, Schalm and Blenis (PDF), Fingar and Blenis (PDF) and Tee and Blenis (PDF).

Sensitized RNAi screen of human kinases and phosphatases identifies novel regulators of apoptosis and chemoresistance.

Evasion from apoptosis is a major cause of cancer and recent success using kinase-targeted therapeutics underscores the importance of identifying cell survival pathways that control apoptosis. We have completed a large-scale RNA interference (RNAi) and a quantitative apoptosis assay to systematically screen all human kinases and phosphatases in cells sensitized with apoptosis-inducing chemotherapeutic agents. In addition to known survival kinases, we have identified several novel kinases, including those regulating the cell cycle or involved in calcium, lipid, TGFβ, tyrosine kinase, and MAPK signaling pathways. Interestingly, a large percentage of phosphatases also contribute to cell survival, revealing a previously unrecognized global role for this gene family as negative regulators of apoptosis. We also identified a novel subset of tumor suppressor-like phosphatases involved in chemosensitivity. Finally, RNAi-mediated down-regulation of individual survival kinases in the presence of submaximal concentrations of paclitaxel (Taxol) potentiates apoptosis. Importantly, this same approach in a resistant breast cancer cell line restores sensitivity to paclitaxel and leads to potent apoptosis. We are currently further characterizing many of these targets with regards to the signaling systems they regulate and the molecular basis of their action. The future development of inhibitors for the kinases identified may lead to novel cancer treatments and facilitate the use of low dose chemotherapy that minimizes toxicity (MacKeigan, Murphy and Blenis (2005) - PDF).