They Might Be Giants: Does Syncytium Formation Sink or Spread HIV Infection?
Fig 2
Host- and virus-mediated regulation of cell—cell fusion during HIV infection.
A simplified schematic is shown of the events shaping HIV Env glycoprotein biosynthesis in the ER and Golgi and the numerous cellular factors encountered along the way. Factors colored in green contribute positively to Env expression, maturation, localization, and/or direct fusogenic capacity, while factors colored in red are inhibitory to one or more of these processes. Arrows and blunt-end lines indicate proteins that promote or inhibit fusion, respectively, between the infected (donor) cell and a neighboring target cell. Question marks are placed where a mechanistic understanding is lacking: GBP5 and 90K expression both lead to the accumulation of gp160 Env, but direct inhibition of gp120–gp41 formation has yet to be demonstrated. Similarly, it is unknown whether SERINC3/5 inhibits Env-mediated cell—cell fusion. TSPN, tetraspanins. IFITM, interferon-induced transmembrane proteins.