Interferon-alfa 2b Activates STAT Proteins in Melanoma Cells

CHICAGO--Although interferon-alfa 2b (Intron A) has been used for sometime to treat malignant melanoma patients at high risk for relapse aftersurgery, little has been known about the way in which it works.

A study from Roswell Park Cancer Institute suggests a possible mechanism.The research, reported at the Society for Surgical Oncology cancer symposium,shows that interferon-alfa 2b activates STAT (signal transducer and activatorof transcription) proteins in malignant melanoma cell lines and tumor specimens.

Using a gel electrophoresis assay, the researchers found that STAT activationwas rapid in melanoma cell lines treated with interferon-alfa 2b, occurringwithin 30 seconds of administration of a radiolabeled DNA probe, said RoswellPark surgeon William Carson, MD.

Pretreatment with genistein, a tyrosine kinase inhibitor, completelyblocked interferon's DNA-binding activity, he added, showing that tyrosinekinase activity is needed for signaling to occur.

Previously frozen melanoma specimens responded to interferon-alfa 2bwith a gel shift on electrophoresis, signaling activation of STAT proteins.Fresh specimens also responded to interferon by generating DNA-bindingactivity.

Interferon-alfa 2b concentrations as low as 102 U/mL activated STAT1 and STAT 2 proteins. A signaling maximum was achieved with a concentrationof 105 U/mL, revealing a distinct dose- response curve for activation ofthese specific STAT proteins.

Pretreatment with interferon-gamma for 18 hours decreased by more than1,000-fold the amount of interferon-alfa 2b needed to activate STAT proteins.The researchers believe interferon-gamma is able to enhance the subsequentresponse to interferon-alfa 2b by acting on the STAT chaperon molecule.

"Interferon-gamma pretreatment has been used with other cytokineswithout much rationale," he said. "The way it is probably workingin this system is by up-regulating levels of the protein chaperon moleculethat carries STAT proteins into the nucleus. There is a gene transcriptionresponse to interferon-gamma, and protein levels come up within a few hours."