Amgen is shedding nearly 500 employees at its Thousand Oaks, Calif., headquarters as it shifts support services to Tampa, Fla., and concentrates research in San Francisco and Cambridge, Mass. Roughly 400 Thousand Oaks staffers will be affected by the opening of a business support center in Tampa. About 50 of them are expected to relocate to the new site. The remaining 100 affected employees are in Amgen’s discovery and translational research unit. Some researchers could move to San Francisco and Cambridge, where Amgen sees more access to innovation.