Research Overview

Cancer and Haematology Division

The Cancer and Haematology Division aims to understand in molecular detail how the production and functions of blood cells are controlled and how these are undermined by blood cell diseases, such as blood cell cancers or leukaemias. For much of its history, the Division concentrated on identifying the blood cell growth factors, their cellular receptors and the consequences of their interactions. In the past few years, our major focus has shifted towards the use of genetic approaches in the mouse, to identify important intracellular signalling molecules and determine their contribution to whole animal biology. Our work also aims to understand the earliest steps in development, where uncommitted embryonic cells decide to become blood cells. A highlight this year has been the tagging of an important gene in this process, so that development of these cells can be monitored.

Background

Differences between CSFs and hormones Hormones are produced in special endocrine glands (e.g. pituitary, adrenal, thyroid) and "broadcast" via the bloodstream to affect target organs. CSFs are synthesised by a wide variety of cells (eg. Fibroblasts or cells lining the blood vessels) anywhere in the body, or from the site of infection or injury.

Around half a century ago, medical researchers began to suspect the existence of a potent hormone-like molecule in the blood that could stimulate unspecialised precursor cells from bone marrow to form granulocytes and macrophages - specialised white blood cells that defend the body against infection by bacteria and viruses.

It's now history that in 1977 Professor Don Metcalf and his colleagues, after 10 years of painstaking research, marked by many setbacks, finally succeeded in purifying the first colony stimulating factor (CSF), granulocyte-macrophage colony stimulating factor (GM-CSF). [For more detail on the discovery and role of CSFs, see the Australian Academy of Science page.]

Virtually since beginning his research career as a postdoctoral scientist in Professor Metcalf's laboratory in 1977, Dr Nic Nicola has been investigating how CSFs regulate the production of red and white blood cells.

"It's the key to understanding what goes wrong in leukaemias and lymphomas," says Dr Nicola.

Colony-stimulating factors are members of the family of cell-to-cell signalling compounds (cytokines) that coordinate haematopoiesis. Secreted into the bloodstream at extremely low concentrations, they stimulate special precursor cells to form the various specialised leucocytes and lymphocytes of the immune system - macrophages, neutrophils, T-cells and B-cells - or the erythrocytes and platelets of the blood system.

CSFs have both routine and emergency roles - they maintain a regular supply of these short-lived cells, or can kick the innate immune system into high gear to deal with invading microbes.

New Directions

Professor Metcalf's team purified and described the first CSFs, sparking enormous international interest in their clinical potential. Two decades on, some of the exceptionally potent cytokines they discovered have entered clinical use. Cytokines like GM-CSF and G-CSF are revolutionising the treatment of cancer and severe infection, and have saved tens of thousands of lives. In the 1990s, they are among the world's most valuable drugs.

The great international cytokine hunt has extended the roll call to more than 100 compounds. "We're still searching for unrecognised or undiscovered CSFs, but we suspect the majority have already been discovered," says Dr Nicola.

"Today we're more interested in how these molecules work. It's one of the major areas of interest in biology.

"How do these extracellular signals tell cells what to do? In terms of therapeutic applications, it's likely to be more fruitful than the study of cytokines themselves.

In therapeutic use, CSFs tend to be blunt instruments, says Dr Nicola - a single CSF can tell a cell to multiply, stop multiplying, differentiate, activate its microbe-killing weaponry, stay alive, or commit suicide.

Instead of sending multiple signals, doctors would prefer to be able to activate specific mechanisms in the target cells: Divide. Stop dividing. Differentiate (change from inactive to active form) and prepare for battle. Or for a cancerous cell: Die!

Cytokine receptors

Recently Dr Nicola's team has turned its attention from CSFs to their receptors. CSFs transmit messages, but it's the receptors on the target cells that ultimately determine what happens inside the cell.

A receptor is a biochemical switch, wired to specific sets of genes in the cell's nucleus through various biochemical circuits. When a CSF molecule plugs into the receptor, it flips the switch and activates (or, sometimes, inactivates) coordinated sets of genes that remodel the cell's phenotype or change its behaviour.

Dr Nicola's team uses site-directed mutagenesis to subtly alter the structure of these switches - particularly in the cytoplasmic domain. By making precise structural changes, then observing any functional changes in the cell's response to a CSF, they can explore the internal signalling pathways in different cell types.

If, for example, the cell loses its ability to differentiate, the researchers know that the mutated domain in the protein controls the differentiation pathway. They can then track down the biochemical pathway that depends on this domain, and ultimately identify the genes that regulate differentiation.

"It's a long, complicated approach, but in the end it reveals the functional elements of pathways that might be targeted with new therapies to treat leukaemias, lymphomas and immune-system disorders," says Dr Nicola.

Knocking out genes

In the past decade, the "knockout mouse" has become a powerful tool for exploring intracellular signalling pathways and determining gene function.

The concept is simple: once a gene of interest has been cloned, researchers deliberately mutate the gene in a transgenic mouse line, then look for any changes in the mouse's phenotype, from which the function of the knocked-out gene can be inferred.

"We use somatic cell genetics to determine the players, and knockout mice to determine the context in which the players normally act," Dr Nicola said.

For example, Dr Glenn Begley's group showed that a genetic mutation in the scl gene causes human lymphoid leukaemia but knockout mice have shown that the correct functioning of this gene is essential for the development of all haematopoietic cells.

LIF and leukaemia

LIF (Leukaemia Inhibitory Factor) was first identified as a cytokine that could force leukaemic cells to differentiate (mature) and then die.

Dr Doug Hilton's team in the CRC for Cellular Growth Factors, has been using somatic cell mutants to explore the LIF receptor signalling pathway. They have used a chemical mutagen to knock out the LIF receptor gene or downstream genes in the LIF pathway; mutant cells are easy to identify - they no longer differentiate in the presence of LIF.

A technique that adds genes, instead of knocking them out, can also be used to explore signalling pathways.

It involves making cDNAs from myeloid cells that cannot differentiate normally, and inserting them singly into normal cells, using a retroviral vector. It these cells lose their ability to differentiate, the transplanted gene presumably makes a protein that blocks differentiation.

The "add-one-gene" technique led Dr Hilton and his colleagues to an entire, new family of signalling proteins called SOCS (suppressors of cytokine signalling) which actively suppress cytokine signalling.

Shared structures, shared functions

Where proteins have overlapping functions (like LIF and IL-6), it's usual that they share structural elements - with proteins, function is closely linked with structure. WEHI's scientists are working with scientists from the Biomolecular Research Institute to determine the three-dimensional structure of cytokines and their receptors. They use X-ray crystallography and nuclear magnetic resonance (NMR) to derive 3-D images of cytokine and receptor molecules in dynamic embrace. By subtly altering the protein molecules with site-directed mutagenesis, researchers can identify which domains are critical to this interaction'

"We learn about these molecules and pathways by disrupting them," Dr Nicola said. "With this knowledge, we can design new drugs to repair pathways that aren't working properly.

"All these pathways are potential targets for new therapies. One day we'll be smart enough to look at a cytokine and its receptor, see which parts are touching, and design a synthetic drug to mimic the cytokine.

Research: what's the attraction?

"We all want to help cure disease, but the bottom line is natural human curiosity," says Dr Nicola. "It's an itch you can't scratch, and it drives you, day in, day out.

"It's just fun coming to work each day. My scientific colleagues are great to work with, and we share a sense of humour as well as a sense of mission."

"Our division is a hive of interesting activities, and there are many ways to make your reputation - we offer young researchers an environment in which they can succeed, if they have the drive.

"We've got some very good scientists to act as mentors, outstanding research facilities, a profile that gets you noticed, and first-class collaborations with other research groups around the world. This is a place where you can become a world class scientist."