<p>Psoriasis is a chronic inflammatory skin disease characterized by excessive keratinocyte proliferation and dysregulated immune responses. The transcriptional regulator AFF3 (ALF transcription elongation factor 3) has recently been implicated in immune-related diseases; however, its role in psoriasis remains unclear. Single-cell sequencing was used to assess AFF3 expression in psoriatic keratinocytes, and immunohistochemical analysis was performed on skin tissue samples from five patients with psoriasis and five healthy controls. A psoriatic inflammation model was established by stimulating HaCaT cells and primary mouse keratinocytes with an M5 cytokine cocktail (IL-17&#xa0;A, IL-22, IL-1α, TNF-α, and oncostatin M). AFF3 expression was quantified by RT-qPCR and Western blotting. AFF3 knockdown was achieved via siRNA-mediated lentiviral transduction, and functional effects were assessed using CCK-8 assay, flow cytometry, and quantification of pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α). Downstream signaling pathways were identified by transcriptomic sequencing, and activation of the MAPK signaling pathway was evaluated by Western blotting. AFF3 expression was elevated in keratinocytes from psoriatic skin lesions compared with normal skin. In both HaCaT cells and primary mouse keratinocytes, AFF3 expression was significantly upregulated following LPS or M5 stimulation. AFF3 knockdown inhibited M5-induced keratinocyte proliferation, increased apoptosis, and reduced oxidative stress, pro-inflammatory cytokine release, and aberrant expression of KRT16, KRT17, and KRT19. Mechanistically, AFF3 knockdown led to decreased phosphorylation levels of ERK, p38, and JNK, indicating suppression of the MAPK signaling pathway. These findings indicate that AFF3 knockdown attenuates keratinocyte hyperproliferation and psoriasis-like inflammatory responses, at least in part, through inhibition of the MAPK signaling pathway.</p>