Scientists have identified four viruses that can produce insulin-like hormones that are active on human cells, thereby opening up possibilities of revealing biological mechanisms that may cause diabetes or cancer.

Every cell in the body responds to the hormone insulin, and if that process starts to fail, you get diabetes. By analysing large public research databases that hold viral genomic sequences, the researchers found that various viruses can produce peptides that are similar in whole or in part to 16 human hormones and regulatory proteins. "We show that these viral insulin-like peptides can act on human and rodent cells," said the study's lead author Emrah Altindis of the Joslin Diabetes Centre, a non-profit institution affiliated with Harvard Medical School.

"We hope that studying these processes will help us to better understand the role of microbes in human disease," Altindis said. The viruses, detailed in the study published in the journal PNAS, were from a family of viruses known to infect fish. To find out if they could be active in mammals, the researchers chemically synthesised these viral insulin-like peptides (VILPs). Experimenting in mouse and human cells, the scientists studied whether the VILPs could act like hormones.

Their experiments proved that the VILPs could indeed bind to human insulin receptors and receptors for a closely-related hormone called IGF-1 (insulin-like growth factor 1). These are the critical proteins on the cells that tell them to take up glucose and to grow. Additionally, the peptides could stimulate all of the signalling pathways inside the cells that were stimulated by human insulin and IGF-1. And mice injected with the viral peptides exhibited lower levels of blood glucose, another sign of insulin action.

Moreover, analysis of databases of viruses found in the human intestine showed evidence that humans are exposed to these viruses, the study said. "Indeed, the discovery of the viral insulin-like hormones raises the question of what their role might be in diabetes, as well as autoimmune disease, cancer and other metabolic conditions," said study senior author C. Ronald Kahn, Professor of Medicine at Harvard Medical School.

"What really caught our attention were four viruses that had insulin-like sequences," Kahn said. The scientists now will broaden their search for other viruses that produce human-like hormones. "We certainly expect to find many more viral hormones, including more viral insulins, in the future," Kahn said.