Calycosin inhibits lytic replication of Kaposi's sarcoma-associated herpesvirus by downregulating early growth...

Kaposi's sarcoma-associated herpesvirus (KSHV) is linked to several diseases, including primary effusion lymphoma, multicentric Castleman's disease, and KSHV inflammatory cytokine syndrome. Current treatment options for KSHV-associated diseases are sometimes ineffective, and antiviral drugs are still lacking. Calycosin (CA), an O-methylated isoflavone found in Astragalus membranaceus, has previously demonstrated strong activity against coxsackievirus B3 (CVB3) and human immunodeficiency virus (HIV), but its effect against KSHV has not been previously reported.

Viral lytic replication was evaluated via both the relative quantification of viral DNA within cells and the absolute quantification of viral genomes in cellular supernatants. RNA sequencing was employed to identify key genes involved in the anti-KSHV process for CA. Real-time PCR and western blotting were utilized to elucidate gene expression. Ectopic gene expression was delivered by plasmid transfection or lentivirus transduction.

CA dose-dependently inhibited KSHV lytic replication in both KSHV latently infected cells and de novo-infected human umbilical vein endothelial cells (HUVECs) without causing cytotoxicity. Further investigation of the anti-KSHV mechanism revealed that CA downregulated the expression of early growth response 1 (EGR1), consequently suppressing the promoter activity of replication and transcription activator (RTA), which is a crucial switch triggering KSHV from latency to lytic replication. Additionally, CA suppressed inflammatory cytokines such as interleukin-6 (IL-6) and interleukin-8 (IL-8) induced by KSHV infection, and this suppression was EGR1 dependent.

This study for the first time reported the function and mechanism of CA in inhibiting the lytic replication of KSHV, providing a new candidate for anti-KSHV agents. Moreover, these findings expand the understanding of the pharmacological values of CA.