The human papillomavirus (HPV) minor capsid protein L2 plays important roles in the generation of infectious viral particles and in the initial steps of infection. Here we show that HPV-16 L2 protein is sumoylated at lysine 35 and that sumoylation affects its stability. Interestingly, the sumoylated form of L2 cannot bind to the major capsid protein L1, suggesting a mechanism by which capsid assembly may be modulated in an infected cell. Additionally, L2 appears to modulate the overall sumoylation status of the host cell. These observations indicate a complex interplay between the HPV L2 protein and the host sumoylation machinery.Posttranslational modification is a central method of diversifying protein function. Ubiquitin-like proteins such as SUMO (small ubiquitin-related modifier) are known to be key regulators of several biological functions (31). In humans, at least three SUMO forms (SUMO1, -2, and -3) are expressed. SUMO2 and SUMO3 (here called SUMO2/3) are closely related, sharing 97% identity, whereas SUMO1 shares 43% identity with SUMO2/3. SUMO modification exerts a variety of effects on its targets, altering a target's cellular localization, its stability, its ability to interact with other proteins, and its activity (31). Most known sumoylation targets are transcription factors or other proteins involved in chromatin structure, regulation, and expression (12), supporting a fundamental role for this modification system in regulating cellular homeostasis. Hence, it is no surprise that viral proteins can exploit the host sumoylation system; proteins from both RNA and DNA viruses have been shown to be sumoylated and/or to interact with the sumoylation machinery (8). The viruses that exhibit interplay between sumoylation and viral proteins can be divided into two groups: viruses that have their proteins sumoylated and viruses whose proteins directly modify host sumoylation. In both cases, the outcome is a cellular environment more favorable for viral replication (5, 8).Human papillomavirus (HPV) infects both mucosal and cutaneous epithelia, and certain high-risk HPV types are the causative agents of cervical cancer (11). Two structural proteins, L1 and L2, form the papillomavirus capsid (16). The minor capsid protein L2 plays a critical role in the generation of infectious viral particles and in early events of HPV infection (13), although its precise functions in HPV entry, intracellular trafficking, endosomal escape, and the nuclear import of the HPV genome have not been fully elucidated (21).Previous studies have shown sumoylation to be important in the HPV life cycle. The functions of two early proteins, E1 and E2, are modified directly by sumoylation (17,19,26,28), and three others, E2 (27), E6 (3), and E7 (14), affect host sumoylation pathways.HPV type 16 (HPV-16) L2's potential involvement with the sumoylation machinery has not been documented, although a consensus sequence, ⌿KXE, where ⌿ is a large hydrophobic amino acid, corresponding to the SUMO acceptor site in most known SUMO substrate proteins...
