Immunology Graduate Program | University of California, San Francisco

Clifford Lowell, MD, PhD

Genetic Analysis of Signal Transduction in Hematopoietic Cells

Professor and Chair, Dept. of Laboratory Medicine
University of California, San Francisco
513 Parnassus Ave, Rm S-1057, Box 0451
San Francisco, CA 94143-0451

(415) 476-2963 tel.
(415) 502-9404 fax
Email

Lab website

AA: Janice Jew, (415) 353-4735

Description of Research

My research group studies the role of cytoplasmic tyrosine kinases in signal transduction pathways within hematopoietic cells. We have focused on the Src-family and Syk tyrosine kinases, which are found in myeloid leukocytes and B-lymphocytes. These proteins play critical roles in transducing signals from cell surface receptors to intracellular targets.

We have taken a genetic approach to study these kinases by generating mutant mice (using embryonic stem cell technology) that lack Hck, Fgr, and Lyn or using Syk-deficient animals. Single mutant mice are interbred to generate double mutant or triple mutant mice, allowing us to address issues of redundancy of function. Mutant animals, and primary cell cultures derived from the mice, are then studied to determine which signaling pathways are affected. Our major finding has been that these kinases function in signaling pathways initiated by integrin-mediated cell adhesion. Integrins are heterodimeric cell surface proteins that mediate attachment of all cells to extracellular matrix protein (i.e., collagen, fibrinogen or fibronectin) coated surfaces. Integrin-dependent adhesion induces an intracellular signaling cascade leading to formation of focal contacts, cytoskeletal rearrangements and cell spreading. In leukocytes, these signaling pathways contribute to immune activation. Both neutrophils and macrophages lacking Src-family kinases or Syk, are completely defective in adhesion mediated activation. This affects the ability of these mice to mount inflammatory responses in vivo.

Src-family kinases also regulate a number of other signaling pathways. Using the knockout mice we have recently made the surprising observation that Hck and Fgr serve as inhibitory kinases to limit myeloid cell activation by chemokines and chemoattractants. This inhibitory pathway is mediated via the ability of these kinases to phosphorylate inhibitory receptors, which in turn activate phosphatases, and other inhibitory molecules that limit intracellular signaling. We have also found that the Lyn kinase plays a paradoxical role in downmodulating signaling from several receptors, including the B-cell receptor and myeloid integrins. Most recently, we have found that the Src-family kinases, Syk and the adapter protein DAP-12 participate in a pathway that limits innate immune responses in macrophages and dendritic cells.

Future projects will include determination of how Syk and other intracellular molecules contribute to integrin signaling, with goal of learning how these pathways lead to leukocyte activation. A major method to study this involves retroviral gene transduction of hematopoietic stem cells, to allow stable expression of mutated kinases and adapters in primary cells from knockout mice. We are also moving towards studying the function of these kinases in limited hematopoietic lineages using Cre-Lox technology to inactivate genes in specific cell types. Ultimately, these studies will provide a better molecular understanding of leukocyte signal transduction, with the hope that therapeutic manipulation of these pathways can be achieved for the treatment of inflammatory or autoimmune disease.

Abram, C.L., Lowell, C.A. (2007) The expanding role for ITAM-based signaling pathways in immune cells. Science STKE. 2007:re2.

Abram, C.L., Lowell, C.A. (2007) Convergence of immunoreceptor and integrin signaling. Immunological Reviews 218:29-44. Download Article

*Zhang, H., Ulrich, S.Y., Green, C.E., Chen, H., Saranto, M.R., Hu, Y., Wara, D., Simon, S.I., Lowell, C.A. (2006) Impaired integrin-dependent function in Wiskott-Aldrich Syndrome Protein-deficient murine and human neutrophils. Immunity. 25:285-295.
* Selected for cover issue and mini-review.

*Mócsai, A., Abram, C.L., Jakus, Z., Hu., Y., Lanier, L.L, Lowell, C.A. , (2006) Integrin signaling in neutrophils and macrophages uses adaptors containing immunoreceptor tyrosine-based activation motifs. Nature Immunol. 12:326-1333.
* Selected for editorial review.

Berton, G., Mocsai, A., Lowell, C.A. (2005) Src kinases and Syk: key regulators of phagocytic cell activation. Trends Immunol., 26, 208-214. Download Article.

Zhang, H., Meng, F., Chu, C-L., Takai, T., Lowell, C.A. (2005) The Src-family kinases Hck and Fgr negatively regulate chemokine signaling in neutrophils and dendritic cells through the inhibitory receptor PIR-B. Immunity, 22,225-246. Download Article

Pereira, S., Zhang, H., Takai, T., Lowell, C.A. (2004) The inhibitory receptor PIR-B negatively regulates neutrophil and macrophage integrin signaling. J. Immunol., 173:5757-5765. Download Article

Mócsai, A., Zhang, H., Jakus, Z., Kitaura, J., Kawakami, T., Lowell, C.A. (2003) G-protein-coupled receptor signaling in Syk-deficient neutrophils and mast cells. Blood 101: 4155-4163. Download Article

Mócsai, A., Zhou, M., Meng, F., Tybulewicz, V.L., Lowell, C.A. (2002) Syk is Required for Integrin Signaling in Neturophils. Immunity 16: 547-558. Download Article