CLDN1 and viral infectious disease: In addition, E2 was also reported to inhibit HCV entry through down-regulation of occludin (OCLN), which is also critical for viral infection (Ulitzky et al., 2016), it can activate GPR30, increase MMP-9 activation and export to the extracellular space leading to cleavage of occludin in Domain D, disrupting occludin-occludin and occludin-claudin-1 interaction.