INSERT INTO myTable (coordinates)
SELECT GeomFromText(CONCAT('POINT(',ot.latitude, ' ', ot.longitude,')'))
FROM otherTable ot;
or
UPDATE myTable
SET coordinates = GeomFromText(CONCAT('POINT(',latitude, ' ', longitude,')'));
INSERT INTO myTable (coordinates)
SELECT GeomFromText(CONCAT('POINT(',ot.latitude, ' ', ot.longitude,')'))
FROM otherTable ot;
or
UPDATE myTable
SET coordinates = GeomFromText(CONCAT('POINT(',latitude, ' ', longitude,')'));