PKIG (cAMP-dependent protein kinase inhibitor gamma) is a potent competitive inhibitor of protein kinase A (PKA) that binds to the catalytic subunit after cAMP-induced dissociation of regulatory chains 1. Located on chromosome 20.12-13.13, PKIG is widely expressed across tissues with highest levels in heart 1. The gene contains conserved pseudosubstrate and nuclear export signal motifs characteristic of the PKI family 1. Mechanistically, PKIG regulates osteoblastic differentiation by suppressing PKA activity; its downregulation is required for BMP-2-induced osteoblast differentiation and bone formation 2. PKIG deletion reciprocally increases osteogenesis while decreasing adipogenesis through modulation of leukemia inhibitory factor (LIF) expression 3. TGF-β2 signaling represses PKIG to enhance PKA/EPAC activation in infected macrophages 4. Clinically, PKIG represents an emerging immunological and prognostic biomarker in lung squamous cell carcinoma, correlating positively with regulatory T cell infiltration and immune checkpoint molecules (PD-1, CTLA-4) 5. PKIG is also implicated in essential thrombocytosis pathogenesis as part of dysregulated miRNA-mRNA networks affecting platelet production 6. PKIG expression responds to metabolic stress and endoplasmic reticulum signaling in glioma cells 7, suggesting relevance to cancer metabolism and stress responses.