The chief executive of e-cigarette maker Juul stepped down on Wednesday as merger talks between its biggest investor Altria and Philip Morris collapsed in the face of a regulatory backlash against vaping that could reshape the industry. Juul Labs, in which tobacco giant Altria Group Inc owns a 35% stake, is facing intense scrutiny in its home market as teen use of e-cigarettes surges. The company, which faces a U.S. ban on some products, said on Wednesday that it would suspend all advertising in the country.