Paolo Ghia, M.D., Ph.D. Instituto Scientifico San Raffaele (Italy)

GENETICS

Dissecting CLL heterogeneity by proteomic analysis

Update:

In the past two years, we have studied the protein expression profile of CLL cells from different subsets of patients. We were hoping to identify therapeutic targets and/or prognostic markers, differentially expressed in CLL patients, which could predict patients with slowly progressing or aggressive disease.

First, we focused our attention on HS1, a protein that we have previously described to be differentially activated in CLL patients. Patients with aggressive disease expressed the protein in a modified (phosphorylated) form. We have now reached several novel conclusions that lay the ground for future intensive research. In particular, we have shown that HS1 is involved in the framework of the leukemic cells. When we completely, or partially, blocked HS1's function in leukemic B-cells, we observed a severe impairment of the CLL cell's ability to migrate. This might indicate that HS1 plays a relevant role in directing cells toward the marrow, as occurs in the late stages of the disease. Interfering with the HS1 protein may produce a potential therapeutic effect. This deserves further studies, which we plan to analyze in our future research activities.

Secondly, we have identified a novel activation site of HS1 that could be used as a target for the production of specific monoclonal antibodies. Specific reagents could be designed to discriminate between the two forms of the protein, thereby predicting patients with a different prognosis. This could be incorporated into a routine diagnostic work-up, using standard methodologies.

Finally, we produced and compared proteomic maps obtained from CLL patients and normal B-cell subpopulations in order to find molecular level differences that could explain the cell's behavior. In particular, we have discovered that 1) a protein (Glo I), involved in cell detoxification, appears to discriminate between patients with a different response to therapy. 2) ZAP-70, a molecule thought to be aberrantly expressed in CLL cells, is actually expressed in all normal B-cell subsets analyzed, and it depends on the activation status of the cells. 3) Cortactin, a protein in epithelial cells, is actually expressed in normal and leukemic B-cells at different levels. All these molecules need further studies to elucidate their importance in CLL.