Intermittently, these Vpr-induced herniations rupture leading to the inappropriate mixing of cellular components that are normally carefully separated between the nucleus and surrounding cytoplasm. This observation is giving clues to how Vpr helps HIV to take over a cell in its effort to conquer an entire immune system.
The study will be published in the Nov. 2 issue of the journal Science.
“We would have not detected these remarkable changes in nuclear envelope structure induced by Vpr if we had not turned to time lapse video microscopy that permits analysis of a single cell over time,” said Warner Greene, MD, PhD, senior co-author, director of the Gladstone Institute of Virology and Immunology, and UCSF professor of medicine, microbiology, and immunology.
Vpr produces these dynamic changes in nuclear architecture by altering the highly ordered structure of a family of proteins termed the nuclear lamins. The lamins form a supporting network of filaments that line the inner surface of the nuclear envelope. “In the presence of Vpr, the structure of the nuclear lamins becomes disorganized,” said lead author Carlos de Noronha, PhD, a research scientist at Gladstone. These changes combine to disable the cell from carrying out vital functions including cell division.
Inhibiting cell division is important to HIV’s cell-conquering strategy. Without cell division, virus production increases by severalfold, greatly improving HIV’s ability to grow. “Then HIV can infect more new target cells leading to faster spread of the infection,” de Noronha said.
The Gladstone research team captured the images by attaching a green or red fluorescent dye to various proteins that govern how the cell divides. One of these proteins is Wee1. During a normal cell cycle, the fluorescent-tagged Wee1 remains confined to the cell nucleus until minutes before cell division occurs. However, in the presence of Vpr, the time lapse videos revealed the transient formation of nuclear herniations containing Wee1 and Vpr that intermittently burst allowing Wee1 and other nuclear proteins to flood into the cytoplasm.
Similarly, cytoplasmic proteins spilled into the nucleus through the newly formed rupture in the nuclear envelope. These intracellular events combine to halt cell division. “These experiments have provided us with an entirely new perspective on how HIV impairs the progression of cells through the normal cell cycle,” Greene said.
Other co-authors include Michael P. Sherman, MD, PhD, Gladstone research scientist; Harrison W. Lin, BA, Gladstone research associate; and Marielle Cavrois, PhD, Gladstone postdoctoral fellow. Other co-authors are Robert D. Goldman, PhD, Stephen Walter Ranson professor and chair of cell and molecular biology; and Robert D. Moir, PhD, research associate professor of cell and molecular biology at Northwestern University Medical School.
The study was funded by the National Institutes of Health and the UCSF-GIVI Center for AIDS Research.
The Gladstone Institute of Virology and Immunology is one of three research institutes that comprise the J. David Gladstone Institutes, a private biomedical research institution affiliated with the University of California, San Francisco. The institutes are named for a prominent real estate developer who died in 1971. His will created a testamentary trust that reflects his long-standing personal interest in medical education and research.
Journal
Science