| Hck (hematopoietic cell kinase) is a myeloid-enriched Src family non-receptor tyrosine kinase that integrates signals from cytokine receptors, Fc receptors, integrins, and oncogenic tyrosine kinases to control proliferation, survival, polarization, and migration of myeloid and B-lineage cells. The protein shares the canonical Src family architecture, with an N-terminal myristoylated and palmitoylated membrane-targeting segment, followed by SH3 and SH2 domains that dock onto proline-rich motifs and phosphotyrosines on partner proteins, and a C-terminal kinase domain whose activity is constrained in the resting state by intramolecular engagement of a phosphorylated C-terminal tyrosine with the SH2 domain; dephosphorylation of this tail and engagement of activating receptors releases the autoinhibited conformation and permits substrate phosphorylation. In myeloid leukemias driven by BCR-ABL, Hck binds the fusion kinase via SH3/SH2 interactions, becomes catalytically activated, and directly phosphorylates STAT5 on its critical activation tyrosine, establishing a BCR-ABL–Hck–STAT5 axis that sustains expression of STAT5 target genes such as A1 and Pim-1 and promotes transformation and cytokine-independent growth of myeloid cells; pharmacologic inhibition or kinase-dead Hck abrogates this STAT5 activation and reduces leukemic cell viability. In acute myeloid leukemia carrying FLT3-ITD mutations, Hck operates downstream of mutant FLT3 and contributes to overexpression and activation of CDK6, linking receptor tyrosine kinase signaling through Hck to Cyclin D–CDK6–Rb control of G1 progression, and defining an essential FLT3–Hck–CDK6 pathway that underlies FLT3-ITD–dependent proliferation and sensitivity to CDK4/6 inhibitors. Hck also participates in the crosstalk between hematopoietic cells and the bone marrow niche through the CXCL12/CXCR4 axis, where its activity modulates adhesion, chemotaxis, and positioning of normal and leukemic progenitors within the marrow microenvironment, providing a mechanistic link between kinase signaling and niche-dependent leukemic cell retention and survival. Increased Hck expression and activity are detected in inflammatory joint and cartilage models, where Hck activation amplifies IL-1β–induced JAK–STAT3 signaling, upregulates IL-6 and TNF-α, promotes chondrocyte apoptosis, and accelerates extracellular matrix degradation, while Hck silencing dampens these responses and preserves tissue architecture, implicating this kinase as a driver of inflammatory tissue damage in osteoarthritis and as a candidate target in chronic joint disease. High HCK expression correlates with distinct transcriptional programs, immune cell infiltration signatures, poorer prognosis, and altered responses to antineoplastic agents, and selective Hck inhibition reduces PI3K/Akt and MAPK/ERK activation after erythropoietin or growth factor stimulation and preferentially induces death of dysplastic and leukemic progenitors while sparing normal hematopoietic stem cells. |
