Preheat oven to 350 degrees. Beat cake mix with water, egg whites and oil. Add dry pudding mix and beat in a large bowl with electric mixer on low speed until moistened. (Batter will be thick.) Beat on medium speed 2 minutes. Spoon batter evenly into 24 paper-lined muffin tins.
Bake 21-24 minutes or until wooden toothpick inserted in centers comes out clean. Cool in pans 10 minutes; remove to wire racks. Cool completely.
Meanwhile, beat sugar, cream cheese, butter and lemon juice with electric mixer on low speed until well blended. Frost cupcakes.