WeWork Cos. said Tuesday that its largest investor, Japanese conglomerate SoftBank Group Corp., has committed an additional $3 billion to the shared-office company, valuing it at about $45 billion

If completed, the deal would make New York-based WeWork—which was last valued in a 2017 fundraising at $20 billion—the second-most valuable U.S. startup behind Uber Technologies Inc., and ahead of Airbnb Inc., according to Dow Jones VentureSource.