Dysfunction in Multiple Myeloma
Mature microRNAs play a critical role in the pathogenesis of solid tumors as well as hematologic malignancies such as multiple myeloma. “Very little is known about the characteristics of multiple myeloma at the epigenetic level,” says Aldo M. Roccaro, M.D., Ph.D., department of medical oncology, Dana-Farber Cancer Institute and Harvard Medical School.
Dr. Roccaro’s goal is to better understand how microRNAs regulate multiple myeloma progression within the bone marrow milieu. “We conducted a series of studies evaluating microRNA signatures in multiple myeloma patients,” he reports. “We showed that plasma cells isolated from patients with multiple myeloma are characterized by lower expression of a specific microRNA cluster called microRNA-17-92, which is located on chromosome 13.”
To perform the studies, Dr. Roccaro and his team investigated 318 microRNAs using liquid-phase Luminex microbead microRNA profiling. In this system, total RNA is labeled with biotin and hybridized to beads containing different fluorophores coated with oligonucleotides complementary to each known microRNA. Binding is detected with streptavidin-phycoerythrin. The team validated its results using quantitative RT-PCR.
“We found a multiple-myeloma-specific signature that was characterized by down expression of a specific set of microRNAs as well as overexpression of another set,” he reports. “We next focused our attention on some of the deregulated microRNAs and looked specifically at microRNA-15a and -16 and how they could potentially regulate myeloma cell growth both in vitro and in vivo. Overall our results suggest that both microRNA-15a and -16 play important roles in the biology of this disease. This information may provide a rationale for developing microRNA-targeted therapies in myeloma.”
Unique Disease Signatures
Rapidly entering the microRNA playing field are strategies to identify altered expression of microRNAs associated with hereditary diseases such as retinitis pigmentosa (RP), the most common form of inherited retinal degenerations. The eye disorder is characterized by progressive photoreceptor-cell death.
According to Arpad Palfi, Ph.D., post-doctoral fellow in the laboratory of G. Jane Farrar, Ph.D., at Trinity College, they generated a microRNA-expression profile in the mouse retina using microRNA microarray technology and real-time RT-PCR.
“Initially, we analyzed a transgenic mouse model in which the gene for rhodopsin has a specific mutation resulting in an RP phenotype,” Dr. Palfi explains. Rhodopsin is a retinal pigment responsible for light detection in rod photoreceptors. Following normalization to wild-type mice, we found an altered microRNA-expression profile involving several microRNAs (e.g., miR-1, -96, -133, and -183) in the rhodopsin-mutant transgenic mice. This data suggested that the normal microRNA expression profile is altered in the disease state.”
The group decided to expand on those studies by examining other RP mouse models. “We examined three RP mouse models using the same strategies and found a common signature in which levels of microRNAs-96, -182, and -183 were decreased while expression of microRNA-1, -133, and -142 were upregulated.”
The group will next examine what protein targets and pathways in the retina are affected by these altered microRNA expression patterns. “If we can understand how microRNAs work in normal and degenerating retinas, perhaps we can use microRNAs as a therapeutic tool, possibly in conjunction with other therapies, to beneficially influence outcome of RP.”
Chronic inflammation is a key feature in many human diseases such as asthma, arthritis, and inflammatory bowel disease. Rene Lutter, Ph.D., principal investigator at the Academic Medical Center, University of Amsterdam, is trying to understand these inflammatory mechanisms and how microRNAs may be implicated.
“Inflammatory processes are tightly controlled at multiple levels to ensure a limited and transient response. The production of mediators such as interleukins and chemokines drive the inflammatory response. A common feature of mRNAs encoding these mediators is the presence of AU-rich elements in the 3´-untranslated region that target the mRNA for rapid degradation.”
Currently, Dr. Lutter and post-doctoral fellow Saheli Chowdhury, Ph.D., are exploring the mechanisms for mRNA degradation of the inflammatory mediators. They manipulate candidate regulatory molecules in cultured airway-epithelial cells and analyze cells derived from the airways of asthmatic and healthy subjects before and after infecting them with rhinovirus 16.
“We see that a family of proteins that binds to these AU-rich mRNA sequences facilitates mRNA degradation,” Dr. Lutter says. Furthermore, it appears that AU-binding proteins act in conjunction with specific microRNAs, targeting a number of mRNAs to modulate production of several inflammatory mediators.”
A key extension of the concept is that aberrant regulation by this system may underlie the development of chronic inflammation. “Recent experiments indicate that manipulating the cellular level of certain microRNAs markedly affects the production of inflammatory mediators. This also suggests their therapeutic potential.”
The young field of microRNA continues to grow and mature. Its enticing potential is driving new strategies and technologies for research, diagnostic, and therapeutic applications.