Gene Switch Takes Blood Cells to Leukemia and Back Again
Loss-of-function mutations in a gene called Pax5 have been known to drive normal blood cells to turn into leukemia cells. Such mutations are permanent, so it remained unclear whether an initial, temporary loss of function would instigate an irreversible cascade of events leading to an accumulation of undifferentiated lymphoblasts, or whether an ongoing loss of function would be needed to maintain the disease state.
With the publication of a new study, the question has become more than academic. The study, by researchers at Melbourne’s Walter and Eliza Hall Institute, has not only shown that switching off Pax5 causes cancer in a murine model of B-progenitor acute lymphoblastic leukemia (B-ALL), it has also demonstrated that switching on Pax5 essentially cures the disease.
The results of the study appeared June 15 in the journal Genes & Development, in an article entitled “Pax5 loss imposes a reversible differentiation block in B-progenitor acute lymphoblastic leukemia.” The article described how the researchers used transgenic RNAi to reversibly suppress endogenous Pax5 expression in the hematopoietic compartment of mice, which cooperates with activated signal transducer and activator of transcription 5 (STAT5) to induce B-ALL.
“In this model, restoring endogenous Pax5 expression in established B-ALL triggers immunophenotypic maturation and durable disease remission by engaging a transcriptional program reminiscent of normal B-cell differentiation,” wrote the authors. “Notably, even brief Pax5 restoration in B-ALL cells causes rapid cell cycle exit and disables their leukemia-initiating capacity.”
Institute researcher Grace Liu noted that Pax5, which is frequently “lost” in childhood B-ALL, is essential for normal development of B cells. “When Pax5 function is compromised, developing B cells can get trapped in an immature state and become cancerous,” she said. “We have shown that restoring Pax5 function, even in cells that have already become cancerous, removes this ‘block,’ and enables the cells to develop into normal white blood cells.”
Simply restoring Pax5 sufficed to normalize cancer cells. That is, re-engaging the stalled differentiation program in immature white blood cells restored normal development “despite the presence of additional oncogenic lesions.”
Institute researcher Ross Dickins, Ph.D., said that forcing B-ALL cells to resume their normal development could provide a new strategy for treating leukemia: “While B-ALL has a relatively good prognosis compared with other cancers, current treatments can last years and have major side effects. By understanding how specific genetic changes drive B-ALL, it may be possible to develop more specific treatments that act faster with fewer side effects.”
“It is very difficult to develop drugs that restore the function of genes that are lost during cancer development,” Dr. Dickins added. “However, by understanding the mechanisms by which Pax5 loss causes leukemia, we can begin to look at ways of developing drugs that could have the same effect as restoring Pax5 function.”
Pax5 is just one of about 100 genes known to suppress human tumors. Now that Pax5 has been scrutinized with genetic switch technology, the researchers speculate that similar technology could be used to characterize other tumor suppressor genes.