A 32-year-old Indian woman presents with a 6-week history of dyspnea, dry cough, and painful red nodules on her shins. Chest X-ray shows the pattern marked **A** in the diagram. Serum calcium is 11.2 mg/dL (normal 8.5–10.5), and transbronchial biopsy reveals non-caseating granulomas. Which of the following best explains the hypercalcemia in this patient?