Building the Foundations of Molecular Biology: RNA Splicing, Gene Regulation and Signaling Pathways
In the last half century scientists have unraveled the workings of genes, proteins, and other large molecules to shed light on how cells transmit their genetic information and to understand the molecular basis of disease. The fundamental contributions of James E. Darnell, Jr., (1930- ) to the new science of molecular biology have launched broad fields of research, shaped nearly all areas of modern cell biology, and guided the search for novel therapies. In the 1960s and early 1970s Darnell's research laid the groundwork for understanding how RNA is spliced as DNA instructions are decoded to make proteins. Two decades later Darnell discovered the relay of molecular signals by which a stimulus outside a cell prods it to turn on specific genes inside its nucleus. One of these pathways, which he mapped in 1992, contributes to certain cancers.
In the early 1960s scientists interested in how the DNA template is converted into proteins studied the relatively simple genes of bacteria. A breakthrough came in 1961, when Jacques Monod and Sidney Brenner discovered messenger RNA (mRNA), the key intermediary molecule in this process. Darnell had spent that year in Monod's Paris laboratory. On returning to the U.S., he sought to find the parallel molecule in animal cells. Using radioactive labeling to identify newly formed RNA, he discovered previously unknown, long, RNA molecules. Comparing these to known ribosomal RNA (rRNA) and mRNA, he found similarities that led him to conclude that these were precursors to the shorter rRNA and mRNA molecules. This set the stage for others to prove that sections of the precursor RNA were spliced out in order to produce the mRNA that directs protein synthesis. Such RNA processing is universal to eukaryotic cells. Today, every biology student learns the fundamental principle that—in contrast to bacteria and viruses—the genes of higher organisms include sections that do not code for proteins, which must be edited out of the RNA intermediary.
Generalized signalling pathway. From Nature Reviews Cancer, 2002, 10: 740-749
Darnell then turned to an equally profound question: how do changes in the environment outside a cell result in the cell altering the genes that are turned on? This process underlies how cells specialize into different types, and communicate with each other, among other tasks. Darnell decided to study interferons, hormones known to quickly stimulate cells to make virus-fighting proteins. Over the next decade he discovered a class of proteins, called transcription factors, that link the binding of interferon to the cell surface to the activation of genes. Darnell named these factors STATs (signal transducers and activators of transcription). Darnell demonstrated that the process has a high degree of specificity, that is, each interferon activates a different set of genes. And he and others elaborated on this finding to show that many different signaling proteins use the JAK-STAT pathway, including molecules such as growth hormone, erythropoietin, and leptin. Other researchers knew that one of the proteins in the JAK-STAT pathway, called Stat3, is activated in many types of cancer, including lymphomas, leukemias, breast cancer, and a high percentage of head and neck cancers. Darnell and his colleagues linked activation of this protein to the development of tumors. Understanding the JAK-STAT pathway provides a basis for developing cancer therapies that shut down Stat3 activity.
James E. Darnell, Jr., received his undergraduate degree at the University of Mississippi and the MD from the Washington University School of Medicine (1955). His career has included poliovirus research with Harry Eagle at the National Institutes of Health, research with François Jacob at the Institut Pasteur in Paris, and academic appointments at the Massachusetts Institute of Technology, the Albert Einstein College of Medicine and Columbia University. In 1974, Darnell joined Rockefeller University as Vincent Astor Professor, and from 1990 to 1991 was vice president for academic affairs. More than 120 doctoral and postdoctoral students have trained in Darnell's laboratory, 50 of whom are full professors and laboratory directors at research institutions throughout the world. A member of the U.S. National Academy of Sciences (1973), Darnell has received numerous awards including the National Medal of Science (2003), the Albert Lasker Award for Special Achievement in Medical Science (2002), the Passano Award (1997), the Paul Janssen Prize in Advanced Biotechnology and Medicine (1994), and the Gairdner Foundation International Award (1986). Darnell is a member of the American Academy of Arts and Sciences and a foreign member of the Royal Society and the Royal Swedish Academy of Sciences. In addition, he is an author of two definitive textbooks: General Virology, with Salvador E. Luria, and Molecular Cell Biology, with Harvey Lodish and David Baltimore.
Scherrer K, Latham H, and Darnell JE. Demonstration of an unstable RNA and precursor to ribosomal RNA in HeLa cells. Proc Natl Acad Sci USA, 1963, 49:240-248
Penman S, Scherrer K, Becker Y, and Darnell JE. Polyribosomes in normal and poliovirus infected HeLa cells and their relationship to messenger RNA. Proc Natl Acad Sci USA, 1963, 49:654-662
Darnell JE, Philipson L, Wall R, and Adesnik M. Polyadenylic acid sequences: Role in conversion of nuclear RNA into messenger RNA. Science, 1971, 174:507-5l0
Darnell JE, Jelinek WR, and Molloy GR. Biogenesis of mRNA: Implications for genetic regulation in mammalian cell. Science, 1973, 181:1215-1221
Levy D and Darnell JE Jr. Interferon-dependent transcriptional activation: signal transduction without second messenger involvement? New Biol, 1990, 2:923-928
Schindler C, Shuai K, Prezioso VR, and Darnell JE Jr. Interferon-dependent tyrosine phosphorylation of a latent cytoplasmic transcription factor. Science, 1992, 257:809-813
Shuai K, Schindler C, Prezioso VR, and Darnell JE, Jr. Activation of transcription by IFN-g: tyrosine phosphorylation of a 91 kD DNA binding protein. Science, 1992, 258:1808-1812
Shuai K, Stark GR, Kerr IM, and Darnell JE Jr. A single phosphotyrosine residue of Stat91 required for gene activation by interferon-?. Science, 1993, 261:1744-1746
Zhong Z, Wen Z, and Darnell JE Jr. Stat3: A STAT family member activated by tyrosine phosphorylation in response to epidermal growth factor and interleukin-6. Science, 1994, 264:95-98
Zhong Z, Wen Z, and Darnell JE Jr. Stat3 and Stat4: Members of the family of signal transducers and activators of transcription. Proc Natl Acad Sci USA, 1994, 91:4806-4810
Darnell JE Jr, Kerr IM, and Stark GM. Jak-STAT pathways and transcriptional activation in response to IFNs and other extracellular signaling proteins. Science, 1994, 264:1415-1421
Schindler C and Darnell JE Jr. Transcriptional responses to polypeptide ligands: the JAK-STAT pathway. Annu Rev Biochem, 1995, 64:621-651
Darnell JE Jr. STATs and gene regulation. Science, 1997, 277:1630-1635
Bromberg JF, Wrzeszczynska MH, Devgan G, Zhao Y, Pestell RG, Albanese C, and Darnell JE Jr. Stat3 as an oncogene. Cell, 1999, 98, 295-303
Shen Y, Devgan G, Darnell JE Jr, and Bromberg JF. Constitutively activated Stat3 protects fibroblasts from serum withdrawal and UV-induced apoptosis and antagonizes the proapoptotic effects of activated Stat1. Proc Natl Acad Sci USA, 2001, 98:1543-1548
Darnell JE Jr. Transcription factors as targets for cancer therapy. Nature Rev Cancer, 2002, 10:740-749
Levy D and Darnell JE Jr. STATs: transcriptional control and biologic impact. Nat Rev Mol Cell Biol, 2002, 3:651-662
Darnell JE Jr. The surprises of mammalian molecular cell biology. Nature Medicine, 2002, 8:1068-1071
Darnell JE Jr. Interferon research: Impact on understanding transcriptional control. Curr Top Microbiol Immunol, 2007, 316:155-163
James E. Darnell, Jr., Laboratory of Molecular Cell Biology
Albert Lasker Award for Special Achievement in Medical Science, 2002
Asking Molecular Biology's Big Questions