A Longstanding Mystery About HIV-1 Nef

HIV-1 has evolved sophisticated strategies to overcome the defenses of the cells it infects. One of its most important accessory proteins, Nef, enhances viral infectivity and contributes to HIV-1 pathogenesis. Although Nef has been studied for decades, the mechanisms underlying some of its activities remain incompletely understood.

Our investigation began with a longstanding puzzle.

Previous studies identified SERINC5 as a cellular restriction factor that reduces HIV-1 infectivity. Nef counteracts SERINC5 by removing it from the cell surface and preventing its incorporation into newly produced viral particles.

However, SERINC5 primarily restricts certain laboratory-adapted HIV-1 strains. Many primary HIV-1 isolates, which more closely resemble viruses circulating in infected individuals, are relatively resistant to SERINC5. Nevertheless, Nef continues to enhance their infectivity.

This discrepancy suggested that another important cellular target of Nef remained unidentified.

We set out to find that missing factor.

An Unexpected Discovery: ADAM17 as a Broad HIV-1 Restriction Factor

We initially investigated cellular proteins associated with SERINC5 using immunoprecipitation coupled with mass spectrometry. Among the candidates were several members of the ADAM protein family, including ADAM9, ADAM15, and ADAM17.

ADAM17, also known as TNF-α-converting enzyme (TACE), is widely recognized for its role in processing cell-surface proteins and releasing inflammatory signaling molecules, including tumor necrosis factor-α (TNF-α). Its established functions are closely connected to immune regulation and inflammation, rather than direct antiviral defense.

To our surprise, ADAM17 strongly inhibited HIV-1 infectivity, whereas the other ADAM family members we examined did not show comparable activity.

Even more importantly, ADAM17 restricted not only laboratory-adapted HIV-1 but also diverse primary isolates representing multiple viral subtypes.

This discovery provided a potential explanation for why Nef remains important across HIV-1 strains that are relatively resistant to SERINC5.

A New Antiviral Mechanism Hidden in a Familiar Protein

Understanding how ADAM17 restricts HIV-1 led to another surprise.

To infect new cells, HIV-1 requires functional envelope glycoproteins. These proteins are initially synthesized as a precursor called gp160, which must undergo proper folding, transport, and cleavage into gp120 and gp41 before being incorporated into infectious viral particles.

We discovered that ADAM17 interacts with gp160 and retains it in the endoplasmic reticulum, preventing its normal oligomerization and transport through the cellular secretory pathway. Consequently, gp160 cannot be efficiently processed into mature envelope proteins, reducing their incorporation into viral particles and impairing infectivity.

Unexpectedly, this antiviral activity does not depend on ADAM17's well-known protease function.

Instead, we identified its short N-terminal signal peptide, approximately 20 amino acids long, as a critical determinant of HIV-1 restriction.

Signal peptides are generally understood as molecular addresses that guide newly synthesized proteins into the appropriate cellular compartment. Our findings reveal an additional, unexpected function for this small region of ADAM17.

Thus, a protein best known for regulating inflammation also possesses a previously unrecognized antiviral activity that targets an early step in HIV-1 envelope maturation.

How Nef Overcomes ADAM17

We next asked whether Nef could counteract this newly identified cellular defense.

Our experiments revealed that Nef promotes the export of ADAM17 from infected cells through extracellular vesicles (EVs), small membrane-bound particles released into the surrounding environment.

This mechanism differs fundamentally from how Nef counteracts SERINC5, which involves intracellular trafficking and degradation.

By promoting ADAM17 export, Nef reduces intracellular ADAM17 levels, thereby relieving the block on gp160 maturation. More mature envelope proteins become available for incorporation into newly produced viral particles, increasing their infectivity.

Using gene-editing approaches in T cells and primary human blood cells, we further demonstrated the biological importance of this mechanism.

For the laboratory-adapted HIV-1 strain NL4-3, both ADAM17 and SERINC5 contribute to Nef-dependent replication. In contrast, for the primary isolates AD8 and BaL, ADAM17 plays the dominant restriction role.

Together, these findings establish ADAM17 as a broad HIV-1 restriction factor and reveal a previously unrecognized mechanism by which Nef enhances viral infectivity.

A New Understanding of Nef in HIV-1 Pathogenesis: One Mechanism, Two Consequences

Perhaps the most exciting implication of our discovery extends beyond viral replication itself.

Our findings support a new model in which Nef-driven ADAM17 export may serve two interconnected functions during HIV-1 infection.

The first function occurs inside infected cells and is directly supported by our experiments. By promoting ADAM17 export in extracellular vesicles, Nef removes a potent restriction on viral envelope maturation, enabling more efficient production of infectious HIV-1 particles.

The second function may occur outside infected cells.

ADAM17 is a major regulator of TNF-α release, an important process in inflammatory signaling. We therefore propose that ADAM17-containing extracellular vesicles released from HIV-1-infected cells may interact with surrounding immune cells, potentially enhancing TNF-α shedding and inflammatory responses.

In this model, Nef could simultaneously remove an antiviral defense from infected cells while promoting pro-inflammatory activity in neighboring, uninfected cells.

This possibility is particularly relevant to one of the major unresolved challenges in HIV medicine.

Although modern antiretroviral therapy can effectively suppress HIV-1 replication, chronic immune activation and inflammation often persist. Elevated inflammatory mediators, including TNF-α, have been associated with HIV-related comorbidities and long-term health complications.

The mechanisms linking HIV-1 infection to persistent inflammation remain incompletely understood.

Our findings raise the possibility that Nef-mediated ADAM17 export provides a molecular connection between viral infectivity and HIV-associated inflammation.

Importantly, our study demonstrates that Nef promotes ADAM17 export and restores viral envelope maturation. Whether ADAM17-containing extracellular vesicles directly enhance TNF-α shedding, amplify inflammatory signaling in bystander cells, or contribute to chronic inflammation in people living with HIV remains to be established.

Nevertheless, this dual-function model offers a new conceptual framework for understanding Nef's contribution to HIV-1 pathogenesis.

Rather than viewing Nef's effects on viral replication and inflammation as entirely separate activities, we can now investigate whether both are connected through a common molecular target.

Looking Ahead: Connecting Viral Fitness With Chronic Inflammation

Our study began with a fundamental virological question: Why does Nef remain important for HIV-1 infectivity when SERINC5 cannot fully explain its activity?

The answer led us to ADAM17, a previously unrecognized cellular restriction factor that blocks HIV-1 envelope maturation.

But the discovery also opened a broader question: Could the same mechanism that enables HIV-1 to overcome an antiviral defense contribute to the persistent inflammation associated with HIV infection?

Future studies will be needed to determine whether ADAM17-containing extracellular vesicles directly influence inflammatory signaling in bystander cells and contribute to HIV-associated disease.

If this connection is established, it could reveal therapeutic opportunities to preserve cellular antiviral defenses while limiting HIV-associated inflammation.

For us, the broader lesson is that studying how a virus overcomes a cellular defense can reveal unexpected connections between viral replication, immune regulation, and disease.

Nef may do more than neutralize a host defense. By promoting ADAM17 export, it may turn that defense into an advantage for the virus—enhancing infectivity inside infected cells while potentially contributing to inflammation beyond them.

Original research: ADAM17 Is a Broad HIV-1 Restriction Factor Targeted by Nef to Restore Env Maturation

Authors: Qiuchen Li, Sunan Li, Shuvankar Dey, Dongjie Sun, Liangliang Sun, and Yong-Hui Zheng

Published article: [https://www.nature.com/articles/s41467-026-78949-0]