Effect of dipicolinate, a chelator of zinc, on bone protein synthesis in tissue culture. The essential role of zinc.

The present investigation was undertaken to clarify the essential role of zinc on bone protein synthesis in tissue culture. Calvariae were removed from 3-week-old male rats and cultured for periods up to 72 hr in Dulbecco's Modified Eagle Medium (high glucose, 4500 mg/dl) supplemented with antibiotics and bovine serum albumin. The calvariae were incubated for 24 hr at 37 degrees in 5% CO2/95% air in medium containing 10(-6)-10(-3) M dipicolinate, a chelator of zinc, and then the bones were transferred into medium containing either 10(-4) M zinc sulfate or vehicle without dipicolinate. Zinc content in bone tissues was decreased when the culture was treated with 10(-4) and 10(-3) M dipicolinate for 24 hr. When calvariae treated with 10(-4) M dipicolinate for 24 hr were further cultured in medium without dipicolinate for 24 and 48 hr, bone alkaline phosphatase activity was decreased by about 40% (P less than 0.01) of untreated bone enzyme activity. The decreased alkaline phosphatase activity was increased markedly by the presence of 10(-4) M zinc (about 2.5-fold of control value). This effect of zinc was blocked completely by the presence of 10(-7) M cycloheximide, but 10(-8) M actinomycin D caused only a partial inhibition. When calvariae treated with 10(-4) M dipicolinate were pulsed with [3H]proline, the incorporation of [3H]proline into the acid-insoluble residues of bone tissue was decreased by about 40% (P less than 0.01) of the value obtained from calvariae not treated with dipicolinate. The presence of 10(-4) M zinc caused an increase of about 2-fold in [3H]proline incorporation. Bone DNA content was not altered significantly by treatment with 10(-4) dipicolinate or 10(-4) M zinc. These results clearly indicate that endogenous zinc induces the stimulation of protein synthesis at the translational process in bone cells. The present study further supports the view that zinc plays an essential role for protein synthesis in bone cells.