FOS and lentivirus infection: Moreover adenovirus and lentivirus infection studies showed that RCAN1-4 is a negative regulator of PGF2α-FP receptor mediated induction of CXCL8 by inhibiting the PGF2α- mediated activation of the AP1 and NFAT cis-acting enhancer elements, similar to our observations for the dn c-Jun and transretinoic acid, giving further support for the co-operativity of NFAT and AP1 in mediating the full transcriptional activation of CXCL8.