Nov 4 (Reuters) - Wall Street's main indexes tumbled on

Tuesday as investors questioned lofty tech valuations after the

CEOs of top Wall Street banks warned of a stock market selloff,

while AI favorite Palantir's sales forecast failed to impress

investors.

The Dow Jones Industrial Average fell 188.6 points,

or 0.40%, at the open to 47,148.04. The S&P 500 fell 63.4

points, or 0.93%, at the open to 6,788.52​, while the Nasdaq

Composite dropped 376.5 points, or 1.58%, to 2,3458.211

at the opening bell.