U.S. scientists identify key protein in immune cells division

WASHINGTON, March 8 (Chinese media) -- U.S. researchers said

on Sunday that they had identified a key protein that is required for immune

cells called B lymphocytes to divide and replicate themselves.

The discovery of the role of the CD98hc protein may

help find new therapy targets for diseases such as multiple myeloma that are

caused by unchecked B cells growth.

Scientists have known for nearly 25 years that

CD98hc, common to all vertebrates, probably played a role in their adaptive

immune system, but it wasn't known how this protein functioned.

"This protein was used as a marker of activation

because it was found in low levels on resting lymphocytes," said first author

Joseph Cantor from the University of California, San Diego School of Medicine.

"But when B or T lymphocytes were stimulated by

antigens - for instance, to protect the body against bacteria - levels of CD98hc

went up 20 fold."

The researchers generated a mouse model lacking the

CD98hc protein in B-lymphocytes. When vaccinated, these mice were unable to

mount a normal antibody response to the pathogen. This was the first clue to the

researchers of the protein's importance, Cantor said.

"In purifying B lymphocytes without the CD98hc

protein, we discovered that the lymphocytes couldn't divide rapidly," he said,

adding that this proved the protein was essential to expanding the number of

immune cells, a necessary step in the immune response.

The researchers speculated that by blocking the

CD98hc protein they could stop the unchecked growth of B lymphocyte cells that

can result in cancer or block misdirected B cell attacks that can cause certain

autoimmune diseases.

The CD98hc protein functions in cells by helping to

transmit integrin signals, as well as transporting amino acids - the building

blocks of proteins - into the cell. But the researchers didn't know which, if

either, of these functions was related to the protein's role in the rapid

division of immune cells.

By replacing normal CD98hc in B cells with a version

that lacked one or the other of these two functions, they discovered that the

integrin-binding domain of this protein is required, but the amino acid

transport function is dispensable for B cell proliferation.

"CD98hc interacts with certain integrin subunits to

prompt signaling events that control cell migration, survival and proliferation.

Our study shows that the rapid proliferation of B cells, necessary for the body

to fight infection, is aided by the CD98hc protein's support of integrin

signaling," Cantor said.

The study is published online on Sunday in advance of

print in the journal Nature Immunology.